Electron-emitting apparatus

ABSTRACT

An electron-emitting apparatus includes an element having a lower electrode, an emitter section composed of a dielectric material, and an upper electrode having a plurality of micro through holes: and a drive voltage applying circuit having a power supply and a circuit that applies a voltage generated by the power supply between the lower electrode and the upper electrode. In order to emit electrons accumulated in the emitter section, the power supply generates a voltage gradually increasing from a first voltage to a second voltage. In order to accumulate electrons In the emitter section, the power supply generates a voltage gradually decreasing from the second voltage to the first voltage. A rapid change in element voltage and excessive element current can thereby be avoided, and unnecessary electron emission can be prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electron-emitting apparatusincluding an emitter section composed of a dielectric material, a lowerelectrode disposed below the emitter section, and an upper electrodedisposed above the emitter section.

2. Description of the Related Art

In the related art, an electron-emitting apparatus including an emittersection composed of a dielectric material, a lower electrode (lowerelectrode layer) disposed below the emitter section, and an upperelectrode (upper electrode layer) disposed above the emitter section andhaving numerous micro trough holes has been known. According to thistype of electron-emitting apparatus, a high-voltage pulse is appliedbetween the upper electrode and the lower electrode to reverse thepolarization of the dielectric material and to thereby emit electronsthrough the micro through holes in the upper electrode (e.g., refer toJapanese Patent No. 3160213, Claim 1, paragraphs 0016 to 0019, and FIGS.2 and 3).

This type of apparatus is applicable to displays. For example, as shownin FIG. 40, the electron-emitting apparatus applied to a displayincludes a transparent plate 17, a collector electrode 18, and phosphors19 above and opposing upper electrodes 14. In the electron-emittingapparatus, the phosphors 19 are irradiated with electrons emitted froman emitter section 13 through micro through holes (not shown) formed inthe upper electrodes 14 and thereby emit light. A predetermined positivevoltage is applied to the collector electrode 18 to thereby acceleratethe emitted electrons.

Light emission caused by the electron emission is controlled as shown inFIG. 41, for example. In particular, from a time t10 to a time t20, theelectron-emitting apparatus set a drive voltage Vin at a negative firstvoltage Vm. The drive voltage Vin is generated by the generated by apower supply and is applied between the upper electrode 14 and a lowerelectrode 12. As a result, the dipole in the emitter section 13 Isreversed (polarization reversal) and electrons are supplied from theupper electrode 14 to the emitter section 13. By this operation, theelectrons are accumulated mainly in regions near the upper portion ofthe emitter section 13. Next, at the time t20, the drive voltage Vin ischanged instantaneously from the first voltage Vm to a positive secondvoltage Vp to again reverse the polarization in the emitter section 13.As a result, electrons accumulated In the emitter section 13 are emittedin the upward direction by Coulomb repulsion caused by the polarizationreversal. The phosphors 19 are thus irradiated with the electrons andemit light.

The electron-emitting apparatus repeats these operations. In otherwords, at the time t30, the drive voltage Vin is instantaneously changedfrom the second voltage Vp to the first voltage Vm to resume electronaccumulation, and at the time t40, the drive voltage Vin isinstantaneously changed from the first voltage Vm to the second voltageVp to again emit electrons to emit light. In this manner, in theconventional electron-emitting apparatus, rectangular pulses are appliedbetween the lower and upper electrode to repeat electron accumulationand electron emission.

SUMMARY OF THE INVENTION

The inventors have found that, immediately after the time t30 (the timeat which the drive voltage Vin is set at the positive second voltage Vpfor electron accumulation) and immediately after the time t40 (the timeat which the drive voltage Vin is set at the positive second voltage Vpfor electron emission), unnecessary emission, such as electron emissionat an unexpected timing and/or excessive electron emission that leads toabnormally intense light emission (extremely strong light emission)sometimes occurs.

The reason for this is unclear, however, may be due to the fact that,from the experiments, a large inrush current flows in the emittersection immediately after the switching of the drive voltage Vin andthat the potential difference (hereinafter also referred to as “elementvoltage”) between the upper electrode and the lower electrodedramatically changes after completion of the polarization reversal inthe emitter section. Emission of abnormally intense light is presumablycaused by dielectric breakdown between the upper electrode 14 and thecollector electrode 18 due to generation of plasma between the upperelectrode 14 and the collector electrode 18. Once such intense lightemission occurs, emission of abnormally intense light may continue dueto continuation of the plasma state.

Unnecessary electron emission decreases the color purity and thecontrast of the Images In the display. Moreover, emission of abnormallyintense light sometimes scatters the materials that constitute the upperelectrode 14 and destroy the upper electrode 14, or even pierces holesin the emitter section 13, thereby damaging the electron-emittingapparatus.

The present invention has been made to overcome the above-describedproblems. It is one of objects of the present invention to avoidunnecessary electron emission by appropriately controlling the voltage(drive voltage) generated by the power supply and/or the parameters ofthe circuit for applying the drive voltage.

To achieve the object, the present invention provides anelectron-emitting apparatus including an element having an emittersection composed of a dielectric material, a lower electrode disposedbelow the emitter portion, and an upper electrode that is disposed abovethe emitter section to oppose the lower electrode with the emittersection therebetween, the upper electrode having a plurality of microthrough holes; and drive voltage applying means having a power supply,and a circuit for applying a voltage, which is generated by the powersupply, between the lower electrode and the upper electrode.

The power supply is configured to generate a first voltage to cause anelement voltage to converge on a negative predetermined voltage so thatelectrons are supplied from the upper electrode to the emitter sectionand accumulated In the emitter section, and to generate subsequently avoltage which gradually increase toward a second voltage to cause theelement voltage to converge on a positive predetermined voltage so thatthe electrons accumulated in the emitter section are emitted from theemitter section, the element voltage being a potential differencebetween the lower electrode and the upper electrode with respect to apotential of the lower electrode.

In the electron-emitting apparatus, the power supply generates a voltagewhich increases gradually when the element voltage is to be set at thepositive predetermined voltage in order to emit electrons. Thus, theinrush current flowing in the emitter section immediately after thestart of the voltage increase by the power supply can be smaller, andthe rate of change in element voltage after completion of thepositive-side polarization reversal can also be smaller. As a result,unnecessary electron emission (unnecessary light emission in case wherea phosphor opposing the upper electrode is provided such as in adisplay) due to the inrush current and unnecessary electron emission(unnecessary light emission) due to the rapid change in element voltageimmediately after the completion of the positive-side polarizationreversal can be avoided.

Moreover, when the voltage (drive voltage) generated by the power supplyis varied as described above, the polarization reversal and the electronemission are caused while the difference between the drive voltage andthe element voltage is small. Thus, power consumption (generation ofjoule heat) by resistor components in the element and a region near theelements can be decreased. As a result, the element is not heated, andthus, the properties of the emitter section can be prevented from beingchanged by the heat. Besides, since the element temperature does notbecome high, evaporation of the materials adhering onto the element canbe avoided. As a result, occurrence of plasma is avoided, and thus,excessive electron emission (intense light emission) as well as damageon the element by ion bombardment can be avoided.

Preferably, the power supply is configured such that, after generationof the first voltage, the power supply generates a voltage increasingfrom the first voltage to a third voltage so that the element voltage iscaused to be an intermediate voltage between the negative predeterminedvoltage and the positive predetermined voltage, the intermediate voltagecausing neither further electron accumulation in nor electron emissionfrom the emitter section; and subsequently, the power supply generates avoltage increasing from the third voltage to the second voltage at arate lower than a rate at which the voltage is increased from the firstvoltage to the third voltage.

Since the polarization reversal in the emitter section does not occurwhen the element voltage is set at the intermediate voltage, neitherfurther electron accumulation in nor electron emission from the emittersection occurs. Furthermore, the unnecessary electron emission does notoccur if the voltage generated by the power supply is caused to increaserelatively rapidly while the element voltage is caused to vary from thenegative predetermined voltage to the intermediate voltage. Accordingly,with the feature described above, the time required from the electronaccumulation to the normal (designed, expected) electron emission can beshortened while avoiding unnecessary electron emission.

Preferably, the power supply is configured such that, within a periodfrom a time point at which generation of the voltage graduallyincreasing toward the second voltage is started to a time point at whichthe voltage reaches the second voltage, the power supply generates avoltage that increases at a lowest rate during a period from the timepoint at which the generation of the voltage gradually increasing towardthe second voltage is started to a time point at which positive-sidepolarization reversal in the emitter section is substantially completed.

The period from “the time point at which generation of the voltagegradually increasing toward the second voltage (from the first or thirdvoltage) is started” to “the time point at which the voltage reaches thesecond voltage” is a period in which the inrush current flowing in theemitter becomes significantly large. Thus, by causing the voltage fromthe power supply to increase at the lowest rate as described above, itis possible to make the inrush current very small. As a result,unnecessary electron emission due to the inrush current can be avoided.Moreover, since the voltage can be gradually increased at a relativelyhigh rate of change from “the time point at which the positive-sidepolarization reversal is completed” to “the time point at which thevoltage from the power supply reaches the second voltage”, it ispossible to shorten the voltage increasing period (the period in which avoltage operation to emit electrons is carried out) which is from thetime point at which the voltage from the power supply is started to beincreased and to the time point at which the voltage from the powersupply reaches the second voltage.

Alternatively, the power supply is configured such that, within a periodfrom a time point at which generation of the voltage graduallyincreasing toward the second voltage is started to a time point at whichthe voltage reaches the second voltage, the power supply generates avoltage that increases at a lowest rate during a period from a timepoint at which positive-side polarization reversal in the emittersection is substantially completed to the time point at which thevoltage reaches the second voltage.

In some elements by themselves or other elements with some measures toavoid unnecessary electron emission, unnecessary electron emission dueto a rapid change in the element voltage upon completion of thepositive-side polarization reversal occurs more frequently than theunnecessary electron emission due to the inrush current. Thus, for suchelements, unnecessary electron emission can be effectively avoided byincreasing the voltage generated by the power supply at a lowest ratefrom the completion of the positive-side polarization reversal to thetime point at which the voltage reaches the second voltage. Moreover,since the voltage generated by the power supply can be graduallyincreased at a relatively high rate during a period from the start ofthe voltage increase to the completion of the positive-side polarizationreversal, it is possible to shorten the voltage Increasing period (theperiod in which a voltage operation to emit electrons is carried out)which is from the time point at which the voltage from the power supplyis started to be increased and to the time point at which the voltagefrom the power supply reaches the second voltage.

The present invention also provides another electron-emitting apparatuscomprising: an element including an emitter section composed of adielectric material, a lower electrode disposed below the emitterportion, and an upper electrode that is disposed above the emittersection to oppose the lower electrode with the emitter sectiontherebetween, the upper electrode having a plurality of micro throughholes; and drive voltage applying means including a power supply and acircuit for applying a voltage, which is generated by the power supply,between the lower electrode and the upper electrode. The power supply isconfigured to generate a second voltage to cause an element voltage toconverge on a positive predetermined voltage so that electronsaccumulated in the emitter section is emitted from the emitter section,and to generate subsequently a voltage which gradually decrease toward afirst voltage to cause the element voltage to converge on a negativepredetermined voltage so that the electrons are supplied from the upperelectrode to the emitter section and accumulated in the emitter section,the element voltage being a potential difference between the lowerelectrode and the upper electrode with respect to a potential of thelower electrode.

In this apparatus, the power supply generates a voltage which decreasesgradually when the element voltage is to be set at the negativepredetermined voltage in order to emit electrons. Thus, the inrushcurrent flowing in the emitter section immediately after the voltagegenerated by the power supply starts to decrease can be smaller, and therate of change in element voltage after completion of the negative-sidepolarization reversal can also be smaller. As a result, unnecessaryelectron emission (unnecessary light emission in case where a phosphoropposing the upper electrode is provided such as in a display) due tothe inrush current and unnecessary electron emission (unnecessary lightemission) due to the rapid change in element voltage immediately afterthe completion of the negative-side polarization reversal can beavoided.

Moreover, when the voltage (drive voltage) generated by the power supplyis varied as described above, the polarization reversal and the electronemission are caused while the difference between the drive voltage andthe element voltage is small. Thus, power consumption (generation ofjoule heat) by resistor components in the element and a region near theelements can be decreased. As a result, the element is not heated, andthus, the properties of the emitter section can be prevented from beingchanged by the heat. Besides, since the element temperature does notbecome high, evaporation of the materials adhering onto the element canbe avoided. As a result, occurrence of plasma is avoided, and thus,excessive electron emission (intense light emission) as well as damageon the element by ion bombardment can be avoided.

Preferably, the power supply is configured such that, after generationof the second voltage, the power supply generates a voltage decreasingfrom the second voltage to a third voltage so that the element voltageis caused to be an intermediate voltage between the negativepredetermined voltage and the positive predetermined voltage, theintermediate voltage causing neither electron accumulation in norelectron emission from the emitter section; and subsequently the powersupply generates a voltage decreasing from the third voltage to thefirst voltage at a rate lower than a rate at which the voltage isdecreased from the second voltage to the third voltage.

When the element voltage is set at the Intermediate voltage, neitherfurther electron accumulation in nor electron emission from the emittersection occurs. Furthermore, the unnecessary electron emission does notoccur if the voltage generated by the power supply is caused to increaserelatively rapidly while the element voltage is caused to become theintermediate voltage. Accordingly, with the feature described above, thetime required from the electron emission to the electron accumulationcan be shortened.

Preferably, the power supply is configured such that, within a periodfrom a time point at which generation of voltage gradually decreasingtoward the first voltage is started to a time point at which the voltagereaches the first voltage, the power supply generates a voltage thatdecreases at a lowest rate during a period from the time point at whichthe generation of the voltage gradually decreasing toward the firstvoltage is started to a time point at which negative-side polarizationreversal in the emitter section is substantially completed.

The period from “the time at which generation of the voltage graduallydecreasing toward the first voltage (from the second or third voltage)is started” to “the time point of the substantial completion of thenegative-side polarization reversal in the emitter section” is a periodin which the inrush current flowing in the emitter becomes significantlylarge. Thus, by causing the voltage from the power supply to decrease atthe lowest rate during this period as described above, it is possible todecrease the inrush current effectively. As a result, unnecessaryelectron emission due to the inrush current can be avoided. Moreover,since the voltage can be gradually decreased at a relatively high rateof change from “the completion of the negative-side polarizationreversal” to “the time point at which the voltage generated by the powersupply reaches the first voltage”, it is possible to shorten the voltagedecreasing period (the period in which a voltage operation to accumulateelectrons) which is from the time point at which the voltage from thepower supply Is started to be decreased to the time point at which thevoltage from the power supply reaches the first voltage.

Alternatively, the power supply may be configured such that, within aperiod from a time point at which generation of voltage graduallydecreasing toward the first voltage is started to a time point at whichthe voltage reaches the first voltage, the power supply generates avoltage that decreases at a lowest rate during a period from a timepoint at which negative-side polarization reversal in the emittersection Is substantially completed to the time point at which thevoltage reaches the first voltage.

In some elements by themselves or other elements with some measures toavoid unnecessary electron emission, unnecessary electron emission dueto a rapid change in element voltage upon completion of thenegative-side polarization reversal occurs more frequently than theunnecessary electron emission due to the inrush current. Thus, for suchelements, unnecessary electron emission can be effectively avoided bydecreasing the voltage generated by the power supply at a lowest ratefrom the completion of the negative-side polarization reversal to thetime point at which the drive voltage reaches the first voltage.Moreover, since the voltage generated by the power supply can begradually decreased at a relatively high rate from the start of thevoltage decrease to the completion of the negative-side polarizationreversal, It is possible to shorten the voltage decreasing period (theperiod in which a voltage operation to accumulate electrons) which isfrom the time point at which the voltage from the power supply isstarted to be decreased to the time point at which the voltage from thepower supply reaches the first voltage.

When repeated electron emission is necessary as when the apparatus isapplied to a display, the power supply is configured to repeatgeneration of the first voltage and the second voltage in an alternatingmanner.

Here, the drive voltage applying means preferably includes circuitparameter setting means for setting a circuit parameter of the circuitby connecting a circuit element to the circuit, the circuit elementbeing selected from the following:

a first circuit element that connects to the circuit during a firstperiod from a time point at which the generation of the voltagedecreasing toward the first voltage is started to a time point at whichthe negative-side polarization reversal in the emitter section issubstantially completed while the voltage is decreased,

a second circuit element that connects to the circuit during a secondperiod from the time point at which the negative-side polarizationreversal in the emitter section is substantially completed to a timepoint at which electron emission in the emitter section is completed,

a third circuit element that connects to the circuit during a thirdperiod from a time point at which generation of the voltage increasingtoward the second voltage is started to a time point at which thepositive-side polarization reversal in the emitter section issubstantially completed while the voltage is increased, and

a fourth circuit element that connects to the circuit during a fourthperiod from a time point at which the positive-side polarizationreversal is substantially completed to a time point at which electronemission from the emitter section is substantially completed. Here, itis preferable that at least two of these circuit elements be differentfrom each other.

During each of the first, the second, the third, and the fourth periods,unnecessary electron emission can take place. However, the period inwhich unnecessary electron emission is frequent differs from oneapparatus from another, depending on the characteristics of the element,the characteristics being determined by the materials and the like, anddepending on other additional measures (such as controlling thecollector electrode) for avoiding the unnecessary electron emission. Inview of this, it is possible to avoid unnecessary electron emission byinserting (connecting) a selected circuit element into the circuit forconnecting the power supply, the upper electrode, and the lowerelectrode so that the parameter of the circuit is constantly set at ahigh value.

However, such an arrangement requires a longer time for electronaccumulation and electron emission, and thus, electron emission at adesired frequency (cycle) is no longer possible. Therefore, as in theabove-described arrangement of the present invention, the circuitelement (e.g., a resistor) to be inserted into (connected to) thecircuit is selectively switched depending on the period so that thecircuit parameter during the period in which the unnecessary electronemission occurs frequently due to the characteristics of the element isdifferent from the circuit parameter during other periods. According tothis arrangement, an electron-emitting apparatus which can emitelectrons at a desired frequency while avoiding unnecessary electronemission is provided. In such a case, the above-described voltagecontrol for gradually increasing or decreasing the voltage generated bythe power supply may or may not be performed.

The present invention also provides another electron-emitting apparatusincluding an element having an emitter section composed of a dielectricmaterial, a lower electrode disposed below the emitter portion, and anupper electrode that is disposed above the emitter section to oppose thelower electrode with the emitter section therebetween, the upperelectrode having a plurality of micro through holes; and drive voltageapplying means having a power supply, and a circuit for applying avoltage, which is generated by the power supply, between the lowerelectrode and the upper electrode.

Here, the power supply, in order to supply electrons from the upperelectrode to the emitter section and to accumulate the electrons in theemitter section, is configured to generate a fourth voltage which is anegative voltage to cause polarization reversal in the emitter section,then to generate a fifth voltage, which is a negative voltage whoseabsolute value is smaller than the absolute value of the fourth voltage,at a time point at which the polarization reversal is substantiallycompleted or before the completion of the polarization reversal, andthen to generate a voltage which gradually decreases toward a firstvoltage and which is a negative voltage whose absolute value is largerthan the absolute value of the fifth voltage.

According to experiments, unnecessary electron emission is frequentlyobserved upon completion of the negative-side polarization reversal thatcauses a rapid change in element voltage. Thus, by controlling thevoltage generated by the power supply as described above, the differencebetween the element voltage and the voltage generated by the powersupply after the negative-side polarization reversal decreases, and thiscauses the element voltage to change gradually with the voltagegenerated by the power supply. Thus, the frequency of the unnecessaryelectron emission can be reduced. Moreover, since the voltage generatedby the power supply until occurrence of the negative-side polarizationreversal is set to the fourth voltage, which is the negative voltagewhose absolute value is larger than that of the fifth voltage, the timetaken until the negative-side polarization reversal can be shortened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of an electron-emittingapparatus according to a first embodiment of the present invention;

FIG. 2 is a partial cross-sectional view of the electron-emittingapparatus shown in FIG. 1, taken along a different plane;

FIG. 3 is a partial plan view of the electron-emitting apparatus shownin FIG. 1;

FIG. 4 Is an enlarged partial cross-sectional view of theelectron-emitting apparatus shown in FIG. 1;

FIG. 5 is an enlarged partial plan view of an upper electrode shown inFIG. 1;

FIG. 6 shows a state of the electron-emitting apparatus shown in FIG. 1;

FIG. 7 is a graph indicating the voltage-polarization characteristic ofan emitter section shown in FIG. 1;

FIG. 8 is a time chart for explaining the operation principle of theelectron-emitting apparatus shown in FIG. 1;

FIG. 9 shows yet another state of the electron-emitting apparatus shownin FIG. 1;

FIG. 10 shows yet another state of the electron-emitting apparatus shownIn FIG. 1;

FIG. 11 shows still another state of the electron-emitting apparatusshown in FIG. 1;

FIG. 12 shows another state of the electron-emitting apparatus shown inFIG. 1;

FIG. 13 shows yet another state of the electron-emitting apparatus shownin FIG. 1;

FIG. 14 is a diagram showing electron emission from an electron-emittingapparatus having no focusing electrode;

FIG. 15 is a diagram showing electron emission from theelectron-emitting apparatus shown in FIG. 1;

FIG. 16 is a time chart showing the drive voltage, element voltage,element current, and optical output of a conventional electron-emittingapparatus during normal electron emission;

FIG. 17 Is a time chart showing the drive voltage, element voltage,element current, and optical output of a conventional electron-emittingapparatus during unnecessary (abnormal) electron emission;

FIG. 18 is a time chart showing the drive voltage, element voltage,element current, and optical output of a conventional electron-emittingapparatus during unnecessary (abnormal) electron emission;

FIG. 19 is a time chart showing the drive voltage, element voltage,element current, and optical output of a conventional electron-emittingapparatus during unnecessary (abnormal) electron emission;

FIG. 20 is a time chart showing the drive voltage, element voltage, andelement current when the waveform of the drive voltage is changed;

FIG. 21 is a time chart showing the drive voltage, element voltage, andelement current when the waveform of the drive voltage is changed;

FIG. 22 is a time chart showing the drive voltage, element voltage,element current, and optical output of the electron-emitting apparatusshown in FIG. 1;

FIG. 23 is a circuit diagram of a drive voltage applying circuit, afocusing electrode potential applying circuit, and a collector voltageapplying circuit shown in FIG. 1;

FIG. 24 is a time chart showing the drive voltage and element voltage ofan electron-emitting apparatus according to a second embodiment of thepresent invention;

FIG. 25 Is a time chart showing the drive voltage and element voltage ofan electron-emitting apparatus according to a third embodiment of thepresent invention;

FIG. 26 is a time chart showing the drive voltage and element voltage ofan electron-emitting apparatus according to a fourth embodiment of thepresent invention;

FIG. 27 is a circuit diagram of an electron-emitting apparatus accordingto a fifth embodiment of the present invention:

FIG. 28 Is a time chart showing the drive voltage of theelectron-emitting apparatus shown in FIG. 27;

FIG. 29 is a time chart showing the drive voltage, element voltage,element current, and optical output of an electron-emitting apparatusaccording to a sixth embodiment of the present invention;

FIG. 30 is a circuit diagram of an electron-emitting apparatus accordingto a seventh embodiment of the present invention;

FIG. 31 is a time chart for explaining the operation of theelectron-emitting apparatus shown in FIG. 30;

FIG. 32 Is a partial cross-sectional view of an electron-emittingapparatus according to an eighth embodiment of the present invention;

FIG. 33 is a partial plan view of a modification example of theelectron-emitting apparatus of the present invention;

FIG. 34 is a partial plan view of another modification example of theelectron-emitting apparatus of the present invention;

FIG. 35 is a partial cross-sectional view of another modificationexample of the electron-emitting apparatus of the present invention;

FIG. 36 is another partial cross-sectional view of the electron-emittingapparatus shown in FIG. 35;

FIG. 37 is a circuit diagram of a measurement circuit for determiningthe relationship between the rising time of the drive voltage and theamount of the electrons emitted:

FIG. 38 is a time chart showing changes in collector current and outputvoltage from an optical output measuring device when the drive voltageis varied;

FIG. 39 is a graph showing the relationship between the amount ofemitted electrons and the intensity of the light output from the opticaloutput measuring device plotted versus the rising time of the drivevoltage varied in various manners;

FIG. 40 is a partial cross-sectional view of an electron-emittingapparatus outside the range of the present Invention; and

FIG. 41 is a time chart showing the drive voltage, collector voltage,and optical output of the electron-emitting apparatus shown in FIG. 40.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Electron-emitting apparatuses according to the preferred embodiments ofthe present invention will now be described with reference to thedrawings. The electron-emitting apparatus is applicable to electron beamirradiators, light sources, manufacturing apparatuses for electroniccomponents, and the like. In the description below, theelectron-emitting apparatuses are applied to displays.

First Embodiment

Structure

As shown in FIGS. 1 to 3, an electron emitting apparatus (an electronemitting device) 10 according to a first embodiment of the presentinvention includes a substrate 11, a plurality of lower electrodes(lower electrode layers) 12, an emitter section 13, a plurality of upperelectrodes (upper electrode layers) 14, insulating layers 15, and aplurality of focusing electrodes (focusing electrode layers, a bundlingelectrode to bundle emitted electrons) 16. FIG. 1 is a cross-sectionalview of the electron emitting apparatus 10 taken along line I-I in FIG.3, which is a partial plan view of the electron emitting apparatus 10.FIG. 2 is a cross-sectional view of the electron emitting apparatus 10taken along line II-II in FIG. 3.

The substrate 11 is a thin plate having an upper surface and a lowersurface parallel to the plane (X-Y plane) defined by the X axis and theY axis perpendicular to each other. The thickness direction of thesubstrate 11 is the Z-axis direction perpendicular to both the X and Yaxes. The substrate 11 is mainly made of zirconium oxide, e.g., glass orceramic.

Each of the lower electrodes 12 is a layer made of a conductivematerial, e.g., silver or platinum in this embodiment, and is disposed(formed) on the upper surface of the substrate 11. In a plan view, eachlower electrode 12 has a shape of a strip, the longitudinal direction ofwhich is the Y-axis direction. As shown in FIG. 1, the adjacent twolower electrodes 12 are apart from each other by a predetermineddistance in the X-axis direction. Note that in FIG. 1, the lowerelectrodes 12 represented by reference numerals 12-1, 12-2, and 12-3 arerespectively referred to as a first lower electrode, a second lowerelectrode, and a third lower electrode for the convenience sake.

The emitter section 13 is made of a dielectric material having a highrelative dielectric constant, or ferroelectric material, for example, athree-component material PMN-PT-PZ composed of lead magnesium niobate(PMN), lead titanate (PT), and lead zirconate (PZ). Materials for theemitter section 13 will be described in greater detail below. Theemitter section 13 is disposed (formed) on the upper surfaces of thesubstrate 11 and lower electrodes 12. The emitter section 13 is a thinplate similar to the substrate 11. As shown in an enlarged view in FIG.4, the upper surface of the emitter section 13 has irregularities(asperity) 13 a formed by the grain boundaries of the dielectricmaterial.

Each of the upper electrodes 14 is a layer made of a conductivematerial, i.e., platinum in this embodiment, and is disposed (formed) onthe upper surface of the emitter section 13. As shown in a plan view ofFIG. 3, each upper electrode 14 has a shape of a rectangle having ashort side and a long side respectively lying in the X-axis directionand the Y-axis direction. The upper electrodes 14 are apart from oneanother and are arranged into a matrix. Each upper electrode 14 isopposed to the corresponding lower electrode 12. In a plan view, theupper electrode 14 is disposed at a position that overlaps thecorresponding lower electrode 12.

Furthermore, as shown in FIG. 4 and FIG. 5, which is a partial enlargedview of the upper electrode 14, each upper electrode 14 has a pluralityof micro through holes 14 a. Note that in FIGS. 1 and 3, the upperelectrodes 14 represented by reference numerals 14-1, 14-2, and 14-3 arerespectively referred to as a first upper electrode, a second upperelectrode, and a third upper electrode for the convenience sake. Theupper electrodes 14 aligned in the same row with respect to the X-axisdirection (i.e., in the same row extending along the Y-axis direction)are connected to one another by a layer (not shown) made of a conductorand are maintained at the same electric potential.

The lower electrodes 12, the emitter section 13, and the upperelectrodes 14 made of a platinum resinate paste are monolithicallyintegrated by firing (baking). As a result of the firing, the upperelectrode 14 shrinks and its thickness of the upper electrode 14reduces, for example, from 10 μm to 0.1 μm. As a result, the microthrough holes 14 a are formed in the upper electrode 14.

The portion where an upper electrode 14 overlaps a corresponding lowerelectrode 12 in a plan view forms one (independent) element for emittingelectrons. For example, the first lower electrode 12-1, the first upperelectrode 14-1, and the portion of the emitter section 13 sandwichedbetween the first lower electrode 12-1 and the first upper electrode14-1 form a first element. The second lower electrode 12-2, the secondupper electrode 14-2, and the portion of the emitter section 13sandwiched between the second lower electrode 12-2 and the second upperelectrode 14-2 form a second element. The third lower electrode 12-3,the third upper electrode 14-3, and the portion of the emitter section13 sandwiched between the third lower electrode 12-3 and the third upperelectrode 14-3 form a third element. In this manner, theelectron-emitting apparatus 10 includes a plurality of independentelectron-emitting elements.

The insulating layers 15 are disposed (formed) on the upper surface ofthe emitter section 13 so as to fill the gaps between the upperelectrodes 14. The thickness (the length in the Z-axis direction) ofeach insulating layer 15 is slightly larger than the thickness (thelength in the Z-axis direction) of each upper electrode 14. As shown inFIGS. 1 and 2, the end portions of each insulating layer 15 in theX-axis direction and the Y-axis direction cover the end portions of theupper electrodes 14 in the X-axis and Y-axis directions, respectively.

Each of the focusing electrodes 16 is a layer made of a conductivematerial, i.e., silver In this embodiment, and are disposed (formed) oneach of the insulating layers 15. As shown in a plan view of FIG. 3,each focusing electrode 16 has a shape of a strip whose longitudinaldirection is the Y-axis direction. Each focusing electrode 16 isdisposed (formed) between the adjacent upper electrodes 14 In the X-axisdirection in the plan view. In detail, each focusing electrode 16 isdisposed between the upper electrodes of the elements adjacent to eachother in the X-axis direction and is slightly obliquely above the upperelectrodes. All the focusing electrodes 16 are connected to one anotherby a layer (not shown) made of a conductor and maintained at the samepotential.

In FIGS. 1 and 3, the focusing electrodes 16 represented by referencenumerals 16-1, 16-2, and 16-3 are respectively referred to as a firstfocusing electrode, a second focusing electrode, and a third focusingelectrode for the convenience sake. The second focusing electrode 16-2lies between the first upper electrode 14-1 of the first element and thesecond upper electrode 14-2 of the second element and is locatedobliquely above the first and second upper electrodes 14-1 and 14-2.Similarly, the third focusing electrode 16-3 is between the second upperelectrode 14-2 of the second element and the third upper electrode 14-3of the third element and is located obliquely above the second and thirdupper electrodes 14-2 and 14-3.

The electron emitting apparatus 10 further Includes a transparent plate17, a collector electrode (collector electrode layer) 18, and phosphors19.

The transparent plate 17 is made of a transparent material (glass oracrylic resin in this embodiment), and is disposed above the upperelectrodes 14 so that the transparent plate 17 is apart from the upperelectrodes 14 in the positive direction of the Z axis by a predetermineddistance. The upper and lower surfaces of the transparent plate 17 areparallel to the upper surfaces of the emitter section 13 and the upperelectrodes 14, and lie in the X-Y plane.

The collector electrode 18 is made of a conductive material. In thisembodiment, the collector electrode 18 is a transparent conductive filmmade of indium tin oxide (ITO) and is formed as a layer covering theentire lower surface of the transparent plate 17. In other words, thecollector electrode 18 is disposed above the upper electrodes 14 and isopposed to the upper electrodes 14.

Each phosphor 19 emits red, green, or blue light by the collision ofelectrons. In a plan view, each phosphor 19 has substantially the sameshape as that of the upper electrode 14 and overlaps the correspondingupper electrode 14. In FIG. 1, the phosphors 19 represented by referencenumerals 19R, 19G, and 19B respectively emit red, green, and blue light.In this embodiment, the red phosphor 19R is disposed directly above thefirst upper electrode 14-1 (i.e., in the positive direction of the Zaxis), the green phosphor 19G is disposed directly above the secondupper electrode 14-2, and the blue phosphor 19B is disposed directlyabove the third upper electrode 14-3. The space surrounded by theemitter section 13, the upper electrodes 14, the insulating layers 15,the focusing electrodes 16, and the transparent plate 17 (the collectorelectrode 18) is maintained under substantial vacuum of preferably 10²to 10⁻⁶ Pa and more preferably 10⁻³ to 10⁻⁵ Pa.

In other words, the side walls (not shown) of the electron emittingapparatus 10, the transparent plate 17, and the collector electrode 18serve as the members for defining a hermetically closed space (anenclosed space), and this hermetically closed space is maintained undersubstantial vacuum. The elements (at least the upper part of the emittersection 13 and the upper electrode 14 of each element) of the electronemitting apparatus 10 are disposed inside the hermetically closed spaceunder substantial vacuum.

As shown in FIG. 1, the electron emitting apparatus 10 further includesa drive voltage applying circuit (drive voltage applying means orpotential difference applying means) 21, a focusing electrode potentialapplying circuit (focusing electrode potential difference applyingmeans) 22, and a collector voltage applying circuit (collector voltageapplying means) 23.

The drive voltage applying circuit 21 has a power supply 21 s forgenerating the drive voltage Vin (described in detail below). The powersupply 21 s is connected to the respective upper electrodes 14 and lowerelectrodes 12. That is, the drive voltage applying circuit 21 comprisesthe power supply 21 s and a circuit that connects the power supply 21 sto the respective elements. The drive voltage applying circuit 21 isalso connected to a signal control circuit 100 and a power circuit 110and applies the drive voltage Vin between the opposing pair of the upperelectrode 14 and the lower electrode 12 (i.e., an element) based on asignal fed from the signal control circuit 100.

The focusing electrode potential applying circuit 22 is connected to thefocusing electrode 16 and applies a predetermined constant negativevoltage (potential) Vs to the focusing electrode 16.

The collector voltage applying circuit 23 applies a predeterminedvoltage (collector voltage) to the collector electrode 18 and includes aresistance 23 a, a switching element 23 b, a constant voltage source 23c for generating a predetermined voltage Vc, and a switch controlcircuit 23 d. One end of the resistance 23 a is connected to thecollector electrode 18. The other end of the resistance 23 a isconnected to a fixed connection point of the switching element 23 b. Theswitching element 23 b is a semiconductor element, such as MOS-FET, andis connected to the switch control circuit 23 d.

The switching element 23 b has two switching points in addition to theabove-described fixed connection point. In response to the controlsignal from the switch control circuit 23 d, the switching element 23 bselectively couples the fixed connection point to one of the twoswitching points. One of the two switching points is grounded, and theother is connected to the anode of the constant voltage source 23 c. Thecathode of the constant voltage source 23 c is earthed. The switchcontrol circuit 23 d is connected to the signal control circuit 100, andcontrols the switching operation of the switching element 23 b based onthe signal received from the signal control circuit 100. Moreover, theswitch control circuit 23 d includes an element voltage measuringcircuit and a detector circuit for detecting completion of electronemission, which will be described below.

Principle and Operation of Electron Emission

The principle of the electron emission of the electron emittingapparatus 10 having the above-described structure will now be explained.To simplify the explanation, in the description below, the drive voltageVin generated by the power supply 21 s is described as rectangular wavesdifferent from the drive voltage Vin of the first embodiment.

First, the state is described with reference to FIG. 6 in which theactual potential difference Vka (element voltage Vka) between the lowerelectrode 12 and the upper electrode 14 with reference to the lowerelectrode 12 is maintained at a predetermined positive voltage Vp and inwhich all the electrons in the emitter section 13 have been emittedwithout remaining in the emitter section 13. At this stage, the negativepole of the dipole in the emitter section 13 is oriented toward theupper surface of the emitter section 13, i.e., oriented in the positivedirection of the Z axis toward the upper electrode 14. This state isobserved at a point p1 on the graph in FIG. 7. The graph in FIG. 7 showsthe voltage-polarization characteristic of the emitter section 13 andhas the abscissa indicating the element voltage Vka and the ordinateindicating the charge Q near the upper electrode 14.

As observed at a time t7 in FIG. 8, the power supply 21 s of the drivevoltage applying circuit 21 decreases the drive voltage Vin toward afirst voltage Vm, which is a negative predetermined voltage. By thisoperation, the element voltage Vka decreases toward a point p3 via apoint p2 In FIG. 7. Once the element voltage Vka is decreased to avoltage near a negative coercive field voltage Va shown In FIG. 7, thereversal of the dipole in the emitter section 13 begins. In other words,as shown in FIG. 9, the polarization reversal (negative-sidepolarization reversal) begins. The polarization reversal increases theelectric field in the contact sites (triple junctions) between the uppersurface of the emitter section 13, the upper electrode 14, and theambient medium (in this embodiment, vacuum) and/or the electric field atthe end portions of the upper electrode 14 forming the micro throughholes 14 a. In other words, electrical field concentration occurs atthese sites. As a result, as shown in FIG. 10, the electrons are startedto be supplied toward the emitter section 13 from the upper electrodes14.

The supplied electrons are accumulated mainly in the upper portion ofthe emitter section 13 near the region exposed through the micro throughhole 14 a and near the distal end portions of the upper electrode 14that define the micro through hole 14 a. This portion where theelectrons are accumulated is hereinafter simply referred to as theregion “near the micro through hole 14 a”. Subsequently, at a time t9 inFIG. 8, the negative-side polarization reversal is completed, and theelement voltage Vka rapidly changes toward the first voltage Vm(negative predetermined voltage), eventually reaching the first voltageVm at a time t10. The electron accumulation is completed as a result,i.e., a saturation state of electron accumulation is reached. This stateis observed at a point p4 in FIG. 7.

At a time t11 shown in FIG. 8, the drive voltage applying circuit 21sets the drive voltage Vin at the a second voltage Vp, which is apositive predetermined voltage. By this operation, the element voltageVka starts to increase. Here, until the element voltage Vka reaches avoltage Vb (point p6) slightly smaller than a positive coercive fieldvoltage Vd corresponding to a point p5 in FIG. 7, the emitter section 13remains charged, as shown In FIG. 11. Subsequently, at a time t13 shownin FIG. 8, the element voltage Vka reaches a voltage near the positivecoercive field voltage Vd. Thus, the negative pole of the dipole startsto orient toward the upper surface of the emitter section 13. In otherwords, as shown in FIG. 12, polarization reversal occurs again, i.e.,the positive-side polarization reversal begins. This state is observednear the point p5 show in FIG. 7.

Subsequently, at a time near a time t14 in FIG. 8 at which thepositive-side polarization reversal is completed, the number of thedipoles having negative poles oriented toward the upper surface of theemitter section 13 increases. As a result, as shown in FIG. 13, theelectrons accumulated near the micro through holes 14 a are started tobe emitted in the upward direction (the positive direction of the Zaxis) through the micro through holes 14 a by Coulomb repulsion.

At a time t14 in FIG. 8, the positive-side polarization reversal iscompleted. The element voltage Vka starts to increase rapidly, andelectrons are actively emitted. At a time t16, electron emission iscompleted, and the element voltage Vka reaches the positivepredetermined voltage Vp. As a result, the state of the emitter section13 is returned to its initial state shown in FIG. 6 observed at thepoint p1 in FIG. 7. This summarizes the principle of a series ofoperation including electron accumulation (light OFF state) and electronemission (light ON or emission state).

Note that, if the electron-emitting apparatus includes two or moreelectron-emitting elements, the drive voltage applying circuit 21 setsthe drive voltage Vin of only the upper electrodes 14 from whichelectron emission is required at the predetermined negative voltage Vmto accumulate electrons, and maintains the drive voltage Vin of upperelectrodes 14 from which no electron emission is required at zero.Subsequently, the drive voltage applying circuit 21 simultaneously setsthe drive voltage of all of the-upper electrodes 14 at the predeterminedpositive value Vp. According to this arrangement, electrons are emittedfrom the upper electrodes 14 (the micro through holes 14 a) of only theelements in which electrons have been accumulated in the emitter section13. Thus, no polarization reversal occurs in the portions of emittersection 13 near the upper electrodes 14 from which no electron emissionis required.

When electrons are emitted through the micro through holes 14 a of theupper electrodes 14, the electrons travel in the positive direction ofthe Z axis by spreading into the shape of a cone, as shown in FIG. 14.Thus, in an apparatus of the related art, electrons emitted from oneupper electrode 14, e.g., the second upper electrode 14-2, reach notonly the phosphor 19, e.g., the green phosphor 19G, directly above thatupper electrode 14 but also the phosphors 19, e.g., the red phosphor 19Rand the blue phosphor 19B, adjacent to this phosphor 19. This decreasescolor purity and sharpness of Images.

In contrast, the electron emitting apparatus 10 of this embodiment hasfocusing electrodes 16 to which a negative potential is applied. Eachfocusing electrode 16 is interposed between the adjacent upperelectrodes 14 (i.e., between the upper electrodes of the adjacentelements) and is disposed at a position slightly above the upperelectrodes 14. Thus, as shown in FIG. 15, the electrons emitted from themicro through holes 14 a travel substantially directly upward withoutspreading owing to the electric field generated by the focusingelectrode 16.

As a result, the electrons emitted from the first upper electrode 14-1reach only the red phosphor 19R, the electrons emitted from the secondupper electrode 14-2 reach only the green phosphor 19G, and theelectrons emitted from the third upper electrode 14-3 reach only theblue phosphor 19B. Thus, the color purity of the display does notdecrease, and sharper images can be obtained.

Unnecessary Electron Emission and Assumption of Reason for Such Emission

In the electron emitting apparatus 10 that operates as described above,it is understood from the collector current (the amount of electronsreaching the collector electrode per unit time) shown in FIG. 8, thatelectron emission starts near the time t14 and reaches the maximumemission per unit time at the time t15. The electron emission iscompleted at the time t16. That is, during this period, proper (regular)emission is observed. However, experiments conducted by the inventorshave reported that unexpected emission (unnecessary electron emission)occurs as described below.

(1) Normal Emission

Firstly, the changes in drive voltage Vin, element voltage Vka, elementcurrent Ik, and optical output APD versus drive voltage Vin that variesin the form of rectangular waves during normal electron emission (lightemission) will be described with reference to FIG. 16. Here, the elementcurrent Ik is current flowing in the portion of the emitter section 13sandwiched between the lower electrode 12 and the upper electrode 14.The optical output APD is a value obtained by converting the emittedlight with an avalanche photodiode. In the graph, the value is indicatedas a negative value.

As shown in FIG. 16, when the drive voltage Vin is risen steeply at thetime t1 so that it is changed from the first voltage (negativepredetermined voltage) Vm to the second voltage (positive predeterminedvoltage) Vp, a large inrush current flows in the emitter section 13.Accordingly, the element current Ik reaches its peak Immediately afterthe time t1 and subsequently reaches zero relatively quickly. On theother hand, between the time t2 to t3 immediately after the time t1, thepositive-side polarization reversal occurs. Thus, the element voltageVka rapidly increases between the time t1 to the time t2 and thenmoderately increases between the time t2 to the time t3. After thepositive-side polarization reversal ends (i.e., the positive coercivefield voltage is exceeded) at the time t3, the element voltage Vkaincreases until the time t4 and becomes equal to the second voltage Vpof the drive voltage Vin thereafter. It is understood from the opticaloutput APD that the electron emission (light emission) starts near thetime t3, reaches the maximum immediately before the time t4, and thenstops.

When the drive voltage Vin is risen steeply so that it is changed fromthe second voltage (positive predetermined voltage) Vp to the firstvoltage (negative predetermined voltage) Vm at the time t5, a largenegative inrush current flows in the emitter section 13. Thus, theelement current Ik reaches its peak immediately after the time t5.Between the time t6 and the time t7 immediately after the time t5, thenegative-polarization reversal occurs. Thus, after a rapid decreasebetween the time t5 and the time t6, the element voltage Vka stayssubstantially constant until the time t7. After the negative-sidepolarization reversal ends (i.e., the negative coercive field voltage isexceeded) at the time t7, the element voltage Vka rapidly decreasesuntil the time t8. At the time t8 and thereafter, the element voltageVka becomes equal to the first voltage Vm of the drive voltage Vin.Meanwhile, the element current Ik rapidly increases toward zero betweenthe time t5 and the time t6, then stays substantially constant until thetime t7, and again rapidly increases toward zero between the time t7 andthe time t8. As can be understood from FIG. 16, no electron is emittedbetween the time t5 and the time t8.

(2) Abnormal Emission (Electron Emission at Inappropriate Timing andExcessive Electron Emission)

Next, the timing of unnecessary electron emission (including excessiveelectron emission) caused by the drive voltage Vin varying in the formof rectangular waves is explained.

Unnecessary electron emission mainly occurs at the following four timepoints:

(A) Referring to a region A1 in FIG. 17, unnecessary electron emissionoccurs immediately after the drive voltage Vin is changed from the firstvoltage Vm which is a negative predetermined voltage (or from thirdvoltage Vn equal to an intermediate voltage applied for non-selection ofelement described below) to the second voltage Vp which is a positivepredetermined voltage. In other words, unnecessary electron emissionoccurs immediately after the time t1 and t11 in FIG. 8 and the time t1in FIG. 16, which is the time point at which the drive voltage VIn isrisen to initiate electron emission. This unnecessary electron emissionis presumably due to a large inrush current (excessively large elementcurrent Ik) flowing between the upper electrode 14 and the lowerelectrode 12, i.e., in the emitter section 13.

(B) Referring to a region A2 in FIG. 17 and FIG. 18, unnecessaryelectron emission occurs immediately after the completion of thepositive-polarization reversal caused by setting the drive voltage Vinto the second voltage Vp. In other words, unnecessary electron emissionoccurs immediately after time t14 in FIG. 8 and time t3 in FIG. 16. Thisunnecessary electron emission is presumably due to a rapid change inelement voltage Vka immediately after the completion of thepositive-side polarization reversal in the emitter section 13, i.e.,immediately after the positive coercive field voltage is exceeded. Inother words, this is presumably due to an excessively large rate ofchange in element voltage Vka over time (dVka/dt).

(C) Referring now to a region A3 in FIG. 17, unnecessary electronemission occurs immediately after the drive voltage Vin is changed fromthe second voltage Vp which is the positive predetermined voltage to thefirst voltage Vm which is the negative predetermined voltage. That is,this unnecessary electron emission occurs immediately after the drivevoltage Vin is rapidly decreased to initiate electron emission (i.e.,immediately after the time t7 and the time t17 in FIG. 8 and the time t5in FIG. 16). This unnecessary electron emission is presumably due to alarge inrush current (excessively large element current Ik) caused bythe rapid change in the drive voltage Vin.

(D) Referring to a region A4 in FIG. 17 and FIG. 19, unnecessaryelectron emission occurs immediately after the completion of thenegative-side polarization reversal caused by setting the drive voltageVin to the first voltage Vm which is the negative predetermined voltage,i.e., immediately after the time t9 and the time t19 in FIG. 8 and thetime t7 in FIG. 16. This unnecessary electron emission is presumably dueto a rapid change in element voltage Vka after completion of thenegative-side polarization reversal in the emitter section 13, i.e., dueto an excessively large rate of change in element voltage Vka over time(dVka/dt).

(3) Relationship Between Rate of Change in Voltage During Period ofIncreasing Drive Voltage Vin, Element Voltage Vka, and Element CurrentIk

Based on the findings above, the inventors have studied thecharacteristics of the element voltage Vka and the element current Ikwhen the drive voltage Vin for electron emission is changed fromrectangular waves to gradually increasing voltage and when the rate ofchange (the rate of change in voltage with respect to timeelasp=dVin/dt) is set at various values.

FIG. 20 includes time charts showing the results of an experiment. InFIG. 20, a line L0 shows a conventional drive voltage Vin in rectangularwaves, a line M0 and a line N0 respectively show the element voltage Vkaand the element current Ik in response to the drive voltage Vinindicated by the line L0. A line L1 shows a drive voltage Vin graduallyincreasing at a predetermined rate α1 of change, i.e., an inclination ordVin/dt. A line M1 and a line N1 respectively represent the elementvoltage Vka and the element current Ik in response to the drive voltageVin indicated by the line L1.

Similarly, a line L2 shows a drive voltage Vin gradually increasing at apredetermined rate α2 of change, and a line M2 and a line N2respectively show the element voltage Vka and the element current Ik inresponse to the drive voltage Vin indicated by the line L2. A line L3shows a drive voltage Vin gradually increasing at a predetermined rateα3 of change, and a line M3 and a line N3 respectively show the elementvoltage Vka and the element current Ik in response to the drive voltageVin indicated by the line L3. Here, α1>α2>α3>0.

As shown in FIG. 20, the peak (maximum value) of the element current Ikis smaller as the rate of change in drive voltage Vin is smaller duringthe period of increasing the drive voltage Vin to conduct electronemission (refer to the portion of the element current Ik circled by adotted line). In particular, it can be understood from the lines L3, M3,and N3 that, by controlling the rate of change in drive voltage Vin sothat the element voltage Vka changes by tracking (i.e., Vka followsclosely to) the changes in drive voltage Vin, the peak of the elementcurrent Ik can be effectively reduced.

(4) Relationship Between Rate of Change in Drive Voltage Vin, ElementVoltage Vka, and Element Current Ik During Period of Decreasing DriveVoltage Vin

The inventor has also studied the characteristics of the element voltageVka and the element current Ik when the drive voltage Vin for electronemission is gradually reduced during the period of accumulating theelectrons in the emitter section. 13, for various rate of change indrive voltage Vin over time.

FIG. 21 includes time charts showing the results of an experiment. InFIG. 21, a line R0 shows a conventional drive voltage Vin that has arectangular falling edge, and a line S0 and a line T0 respectively showthe element voltage Vka and the element current Ik in response to thedrive voltage Vin shown by the line R0. A line R1 shows a drive voltageVin gradually decreasing at a predetermined rate β1 of change, i.e., apredetermined inclination or |dVin/dt |, and a line S1 and a line T1respectively show the element voltage Vka and the element current Ik Inresponse to the element voltage Vka shown by the line R1.

Similarly, a line R2 shows a drive voltage Vin gradually decreasing at apredetermined rate β2 of change (|dVin/dt|), and a line S2 and a line T2respectively indicate the element voltage Vka and the element current Ikin response to the drive voltage Vin shown by the line R2. A line R3shows a drive voltage Vin gradually decreasing at a predetermined rateβ3 of change (|dVin/dt|), and a line S3 and a line T3 respectivelyindicate the element voltage Vka and the element current Ik in responseto the drive voltage Vin indicated by the line R3. Here, β1>β2>β3>0.

As shown in FIG. 21, the peak (maximum value) of the element current Ikis smaller as the rate of change in drive voltage Vin is smaller duringthe period of decreasing the drive voltage Vin to conduct electronaccumulation (refer to the portion of the element current Ik circled bya dotted line). Moreover, the rate of change in element voltage Vkaafter completion of the negative-side polarization reversal decreasesslightly as the rate of change in drive voltage Vin is decreased (referto the portion of the element voltage Vka circled by a alternate longand short dash line).

Control of Drive Voltage

Based on the results of the experiments described above, the drivevoltage applying circuit 21 according to the first embodiment generatesa drive voltage Vin having a characteristic shown in FIG. 22.Specifically, the power supply 21 s of the drive voltage applyingcircuit 21 starts to increase the drive voltage Vin from the firstvoltage Vm (which is the negative predetermined voltage) at a particulartime (time t1 shown in FIG. 22). The power supply 21 s graduallyincreases the drive voltage Vin at a predetermined rate α(=dVin/dt>0) sothat the drive voltage Vin reaches the second voltage Vp (which is thepredetermined positive voltage) at a time t4 after the start of thepositive-side polarization reversal (time t2) and the completion of thepositive-side polarization reversal (time t3 at which the positivecoercive field voltage is exceeded).

With the drive voltage Vin above, the inrush current (the peak value ofthe element current Ik) that occurs during the electron emission causedby the increased drive voltage Vin can be reduced, and the rapid changein element voltage Vka that would occur after the completion of thepositive-side polarization reversal can be avoided. As a result,unnecessary electron emission that occurs during the period ofincreasing the drive voltage Vin can be avoided.

At a particular time (t5) after the completion of the electron emission(time t4), the power supply 21 s of the drive voltage applying circuit21 starts to decrease the drive voltage Vin from the second voltage Vpat a predetermined rate β of change so that the drive voltage Vinreaches the first voltage Vm after the start of the negative-sidepolarization reversal (time t6) and completion of the negative-sidepolarization reversal (time t7 at which the negative-side coercive fieldvoltage is exceeded).

With the drive voltage Vin above, the inrush current (the peak value ofthe element current Ik) that occurs during the electron accumulationcaused by decreasing drive voltage Vin can be reduced, and the rapidchange in element voltage Vka after the negative-side polarizationreversal can be avoided. As a result, unnecessary electron emissionduring the period of decreasing the drive voltage Vin can be avoided.

Control of Collector Electrode

The collector voltage applying circuit 23 applies a second collectorvoltage V2 to the collector electrode 18 so that the collector voltageis changed from the first predetermined voltage to a secondpredetermined voltage smaller than the first predetermined voltage at aparticular time point within the period from immediately after the timet4 to the time t5 in FIG. 22. Here, “immediately after the time t4”means the time point at which the electron emission through the microthrough holes 14 a caused by changing the drive voltage Vin toward thesecond voltage Vp (predetermined positive voltage) is substantiallycompleted. The time t5 is the time at which drive voltage Vin starts todecrease from the second voltage Vp which is the predetermined positivevoltage. That is, the collector voltage applying circuit 23 switches theconnecting point to which the fixed connection point of the switchingelement 23 b is connected from the switching point connected to theconstant voltage source 23 c to the earthed switching point.

Note that the switching element 23 b may be configured such that theearthed switching point is replaced by a floating point coupled tonowhere. In this case, the collector electrode 18 is caused to enter afloating state, by a switching operation in which the point coupled tothe fixed connection point is switched from the switching point coupledto the constant voltage source 23 c to the switching point in thefloating state. Here, both the operation in which the second collectorvoltage V2 is applied to the collector electrode 18 by earthing(grounding) the collector electrode 18 and the operation in which thecollector electrode 18 is put under a floating state are each referredto as “turning the collector electrode off” hereinafter.

When the collector electrode 18 is turned off, the collector electrode18 does not generate an electric field that attracts the emittedelectrons or the collector electrode 18 decreases the Intensity of suchelectric field. As a result, unnecessary electron emission (andunnecessary light emission) can be avoided.

Subsequently, the collector voltage applying circuit 23 switches theconnecting point to which the fixed connection point of the switchingelement 23 b Is connected from the earthed switching point to theswitching point connected to the constant voltage source 23 c at aparticular time within a period from the time t8 in FIG. 22 to the timebefore the completion of the next electron emission. Here, the time t8is a time at which electron accumulation by changing the drive voltageVin to the first voltage Vm is substantially completed. In other words,the collector voltage applying circuit 23 resumes application of thefirst collector voltage V1 (Vc) to the collector electrode 18 at thisparticular time. This time point is also referred to as the “collectorelectrode ON time” for the convenience sake.

By this operation, the emitted electrons are accelerated (i.e., givenhigh energy) by the electric field generated by the collector electrode18 and travel in the upward direction from the upper electrode 14. Thus,the phosphors 19 are irradiated with electrons having high energy, andtherefore, high luminance is achieved. In other words, since thecollector electrode 18 to which the first collector voltage V1 isapplied attracts the emitted electrons, a desired amount of electronscan reach near the collector electrode 18.

By controlling the collector electrode 18 as such, at least during theperiod from the start of the voltage decrease to the completion of theelectron accumulation, either the collector voltage is maintained at thesecond predetermined voltage (in this embodiment, 0 V, which is theground potential) or the collector electrode is maintained in thefloating state.

As a result, unnecessary electron emission presumably caused by a largeinrush current flowing in the emitter section 13 during the electronaccumulation can be securely avoided. Moreover, unnecessary electronemission presumably resulting from a high rate of change in elementvoltage Vka occurring Immediately after completion of the negative-sidepolarization reversal can be securely avoided.

The collector electrode ON time may be set as follows:

(a) The collector electrode ON time may be set at a time point (t10 inFIG. 22) at which the drive voltage Vin starts to increase from thefirst voltage Vm toward the second voltage Vp.

According to the collector electrode ON time in the case (a) above,unnecessary electron emission during the electron accumulation (from t5to t10 in FIG. 22) can be avoided. Furthermore, since the firstcollector voltage is applied to the collector electrode 18 over theentire period in which the drive voltage Vin is increasing for electronemission, the electron normally emitted can be led to the collectorelectrode 18. In addition, since the time point at which the drivevoltage Vin starts to increase is coincident with the time point atwhich the first collector voltage is applied to the collector electrode,the circuit configuration for this operation can be simplified.

(b) The collector electrode ON time may be set at a particular timebetween the time point at which the inrush current in the emittersection 13 reaches the maximum by the increase of the drive voltage Vintoward the second voltage Vp and the time point at which thepositive-side polarization reversal is completed.

According to the collector electrode ON time in the case (b) above,unnecessary electron emission during the electron accumulation (from t5to t10 in FIG. 22) and unnecessary electron emission resulting from alarge inrush current at the time of increasing the drive voltage Vin canbe avoided. In addition, after the completion of the positive-sidepolarization reversal, the first collector voltage is applied to thecollector electrode. Thus, the electrons normally emitted after thepositive-side polarization reversal can be led toward the collectorelectrode.

(c) The collector electrode ON time may be set at a particular timebetween the completion of the positive-side polarization reversal andthe substantial completion of the electron emission.

According to the collector electrode ON time in the case (c) above,unnecessary electron emission during the electron accumulation (from t5to t10 in FIG. 22) can be avoided. Moreover, It is possible to avoidunnecessary electron emission due to an inrush current and the likebefore the completion of the positive-side polarization reversal whilethe drive voltage Vin is increasing. Besides, at the time point beforethe completion of the electron emission, the first collector voltage isapplied to the collector electrode. Thus, the electrons normally(properly) emitted can be led to the collector electrode. Furthermore,since the first collector voltage is applied to the collector electrodesubstantially only during the designed electron emission period,excessive electron emission can be effectively suppressed.

(d) The collector electrode ON time may be set at a particular timebetween the completion of the positive-side polarization reversal andthe time point at which the amount of the electrons emitted from theemitter section and reaching the collector electrode (the currentflowing in the collector electrode) reaches per unit time the maximum.

According to the collector electrode ON time in the case (d) above,unnecessary electron emission during the electron accumulation (t5 tot10 in FIG. 22) can be avoided. Moreover, It is possible to avoidunnecessary electron emission due to an inrush current and the likebefore the completion of the positive-side polarization reversal whilethe drive voltage Vin is increasing. Besides, after the current flowingin the collector electrode reaches the maximum, the first collectorvoltage is applied to the collector electrode. Thus, the electronsnormally (properly) emitted can be securely led to the collectorelectrode. In other words, it becomes possible to ensure the requiredamount of electron emission while avoiding excessive electron emission.

(e) The collector electrode ON time may be set to the time point atwhich the actual element voltage Vka reaches a predetermined thresholdvoltage Vth while the drive voltage Vin is being increased. In thiscase, the predetermined threshold voltage Vth is preferably selectedsuch that the collector electrode ON time falls in between the timepoint of the completion of the positive-side polarization reversal andthe time point at which the current flowing the collector electrodereaches the maximum.

According to the collector electrode ON time in the case (e) above,unnecessary electron emission during the electron accumulation (t5 tot10 in FIG. 22) can be avoided. Moreover, unnecessary electron emissiondue to an inrush current and the like at the start of the increase ofthe drive voltage Vin can be avoided. In addition, since the elementvoltage Vka varies depending on the images (the amount of electronsrequired to be emitted) to be displayed, the collector electrode can beturned on at an appropriate timing despite the manner in which theelement voltage Vka changes. Here, said “appropriate timing” is one thatcan lead as many electrons normally emitted as possible to the collectorelectrode while suppressing unnecessary electron emission.

Specific Examples of Drive Voltage Applying Circuit, Focusing ElectrodePotential Applying Circuit, and Collector Voltage Applying Circuit

The specific examples and operation of the drive voltage applyingcircuit 21, the focusing electrode potential applying circuit 22, andthe collector voltage applying circuit 23 will now be explained.

As shown in FIG. 23, the drive voltage applying circuit 21 includes arow selection circuit 21 a, a pulse generator 21 b, and a signalsupplying circuit 21 c. In FIG. 23, the components labeled D11, D12, . .. D22, and D23 each represent one element, i.e., an electron-emittingelement (one element constituted from the portion where upper electrode14 is superimposed on the lower electrode 12 with the emitter section 13therebetween). In this embodiment, the electron emitting apparatus 10has a number n of elements in the row direction and a number m ofelements In the column direction.

The row selection circuit 21 a is connected to a control signal line 100a of the signal control circuit 100 and a positive electrode line 110 pand a negative electrode line 110 m of the power circuit 110. The rowselection circuit 21 a is also connected to a plurality of row selectionlines LL. Each row selection line LL is connected to the lowerelectrodes 12 of a series of elements in the same row. For example, arow selection line LL1 is connected to the lower electrodes 12 ofelements D11, D12, D13, . . . and D1 m in the first row, and a rowselection line LL2 is connected to the lower electrodes 12 of elementsD21, D22, D23, . . . and D2 m in the second row.

During the charge accumulation period Td in which electrons areaccumulated in the emitter section 13 of each element, the row selectioncircuit 21 a outputs a selection signal Ss (a 50-V voltage signal inthis embodiment) to one of the row selection lines LL for apredetermined period (row selection period) Ts and outputs non-selectionsignals Sn (a 0-V voltage signal in this embodiment) to the rest of therow selection lines LL in response to the control signal from the signalcontrol circuit 100. The row selection line LL to which the selectionsignal Ss is output from the row selection circuit 21 a is sequentiallychanged every period Ts.

The pulse generator 21 b generates a reference voltage (0 V in thisembodiment) during a charge accumulation period Td and a predeterminedfixed voltage (−400 V in this embodiment) during an emission period(electron emitting period or light ON period) Th. The pulse generator 21b is coupled between the negative electrode line 110 m of the powercircuit 110 and the ground (GND).

The signal supplying circuit 21 c is connected to the a control signalline 100 b of the signal control circuit 100 and the positive electrodeline 110 p and the negative electrode line 110 m of the power circuit110. The signal supplying circuit 21 c has a pulse generating circuit 21c 1 and an amplitude modulator circuit 21 c 2 inside.

The pulse generating circuit 21 c 1 outputs a pulse signal Sp having apredetermined amplitude (50 V in this embodiment) at a predeterminedpulse period during the charge accumulation period Td, and outputs areference voltage (0 V in this embodiment) during the emission periodTh.

The amplitude modulator circuit 21 c 2 is connected to the pulsegenerating circuit 21 c 1 so as to receive the pulse signal Sp from thepulse generating circuit 21 c 1. Further, the amplitude modulatorcircuit 21 c 2 is connected to a plurality of pixel signal lines UL.Each pixel signal line UL is connected the upper electrodes 14 of aseries of elements in the same column. For example, a pixel signal lineUL1 is connected to the upper electrodes 14 of the elements D11, D21, .. . and Dn1 of the first column, a pixel signal line UL2 is connected tothe upper electrodes 14 of the elements D12, D22, . . . and Dn2 of thesecond column, and a pixel signal line UL3 is connected to the upperelectrodes 14 of the elements D13, D23, . . . and Dn3 of the thirdcolumn.

During the charge accumulation period Td, the amplitude modulatorcircuit 21 c 2 modulates the amplitude of the pulse signal Sp accordingto the luminance levels of the pixels in the selected row, and outputsthe modulated signal (a voltage signal of 0 V, 30 V, or 50 V in thisembodiment), which serves as a pixel signal Sd, to the pixel signallines UL (UL1, UL2, . . . and ULm). During the emission period Th, theamplitude modulator circuit 21 c 2 outputs, without any modulation, thereference voltage (0 V) generated by the pulse generating circuit 21 c1.

The signal control circuit 100 receives a video signal Sv and a syncsignal Sc and outputs a signal for controlling the row selection circuit21 a to the signal line 100 a, a signal for controlling the signalsupplying circuit 21 c to the signal line 100 b, and a signal forcontrolling the collector voltage applying circuit 23 to a signal line100 c based on these received signals.

The power circuit 110 outputs voltage signals to the positive electrodeline 110 p and the negative electrode line 110 m so that the potentialof the positive electrode line 110 p is higher than the potential of thenegative electrode line 110 m by a predetermined voltage (50 V in thisembodiment).

The focusing electrode potential applying circuit 22 is coupled to aconnecting line SL that connects all of the focusing electrodes 16. Thefocusing electrode potential applying circuit 22 applies to theconnecting line SL a potential Vs (e.g., −50 V) with respect to theground.

The collector voltage applying circuit 23 is connected to aninterconnection line. CL coupled to the collector electrode 18 and thesignal line 100 c of the signal control circuit 100. The collectorvoltage applying circuit 23 alternately applies the positive firstvoltage Vc (first collector voltage V1) and the second voltage (thesecond collector voltage V2, which is the ground voltage, 0 V, in thisembodiment) smaller than the first voltage Vc to the interconnectionline CL based on the signal fed from the signal control circuit 100.

The operation of the circuit having the above-described structure willnow be described. At initiation of the charge accumulation period Tdstarting at a particular time, the row selection circuit 21 a outputs aselection signal Ss (50 V) to the row selection line LL1 of the firstrow based on the control signal from the signal control circuit 100 andoutputs non-selection signals Sn (0 V) to the rest of the row selectionlines LL. As this time, the row selection circuit 21 a sets the rate ofchange in voltage for the selection signal Ss supplied to the rowselection line LL1 to a predetermined value (|dV/dt| or thepredetermined rate of change in voltage) β. In particular, the rowselection circuit 21 a gradually increases the voltage from 0 V to 50 Vat a rate β of change in voltage and applies to the row selection linethe selection signal Ss, which is the voltage maintained at 50 V. As aresult, the potential of the lower electrodes 12 of the elements D11,D12, D13, . . . and D1 m in the first row becomes the voltage (50 V) ofthe selection signal Ss. The potential of the lower electrodes 12 of theother elements, for example, the elements D21, D22, . . . and D2 m inthe second row and the elements D31, D32, . . . and D3 m in the thirdrow, becomes the voltage (0 V) of the non-selection signal Sn.

At this time, the signal supplying circuit 21 c outputs pixel signals Sd(0 V, 30 V, or 50 V In this case) to the pixel signal lines UL (UL1, UL2. . . and ULm) based on the control signal from the signal controlcircuit 100. The pixel signals Sd correspond to the luminance level ofthe respective pixels constituted from the elements of the selected row,i.e., in this case, the elements D11, D12, D13, . . . and D1 m In thefirst row.

For example, assuming that a 0-V pixel signal Sd is supplied to thepixel signal line UL1, the element voltage Vin(D11) of the upperelectrode 14 of the element D11 with respect to the lower electrode 12of the same element becomes eventually (converges on) the aforementionednegative predetermined voltage Vm, i.e., −50 V(=0 V−50V). A large numberof electrons are thus accumulated in the emitter section 13 near theupper electrode 14. Assuming that a 30-V pixel signal Sd is supplied tothe pixel signal line UL2, the element voltage Vka(D12) of the upperelectrode 14 of the element D12 with respect to the lower electrode 12of the same element converge on the aforementioned negativepredetermined voltage Vm, i.e., −20 V (=30 V−50 V). As a result, fewerelectrons are stored in the emitter section 13 of the element D12 nearthe upper electrode 14 than in the element D11.

Note that, since the selection signal Ss is a voltage that graduallyincreases from 0 V to 50 V at a rate β of change in voltage, the drivevoltage Vin applied to these elements gradually decreases toward thefirst voltage Vm, i.e., the negative predetermined voltage, and is thenmaintained at the first voltage Vm.

Assuming that a 50-V pixel signal Sd is supplied to the pixel signalline UL3, the element voltage Vka(D13) of the element D13 is 0 V (=50V−50 V). Thus, no electrons are accumulated in the emitter section 13 ofthe element D13, and no polarization reversal occurs in the emittersection 13 of the element D13.

When the row selection period Ts (the period sufficient for accumulatingelectrons in the selected element, e.g., the period from the time t6 tothe time t10 shown In FIG. 22) elapses, the row selection circuit 21 aoutputs the selection signal Ss (a voltage gradually increasing from 0 Vto 50 V at a rate β) to the row selection line LL2 for the second rowbased on the control signal fed from the signal control circuit 100 andoutput the 0-V non-selection signals Sn to the rest of the row selectionlines LL. By this operation, the potential of the lower electrodes 12 ofthe elements D21, D22, D23, . . . and D2 m in the second row becomes thevoltage (50 V) of the selection signal Ss. The potential of the lowerelectrodes 12 of the rest of the elements (e.g., the elements D11 to D1m in the first row and the elements D31 to D3 m in the third row)becomes the voltage (0 V) of the non-selection signals Sn.

Meanwhile, the signal supplying circuit 21 c outputs pixel signals Sd (0V, 30 V, or 50 V in this embodiment) to the pixel signal lines UL (UL1,UL2, . . . and ULm) based on the control signal from the signal controlcircuit 100. The pixel signals Sd correspond to the luminance levels ofthe respective pixels constituted from the elements of the selected row,i.e., in this case, the elements D21, D22, D23, . . . and D2 m in thesecond row. As a result, electrons are accumulated in the emittersections of the elements D21, D22, D23, . . . and D2 m in the secondrow, in amounts corresponding to the pixel signals Sd.

Note that the element voltage Vka of each element having the lowerelectrode with a 0-V non-selection signal Sn applied thereto is 0 V (thepotential of the upper electrode: 0 V, the potential of the lowerelectrode: 0 V), 30 V (the potential of the upper electrode: 30 V, thepotential of the lower electrode: 0 V), or 50 V (the potential of theupper electrode: 50 V, the potential of the lower electrode: 0 V).However, this level of voltage does not cause polarization reversal inthe element in which the electrons are already accumulated and thus doesnot cause electron emission from that element.

The drive voltage Vin for the element connected to the row selectionline LL1 to which the selection signal Ss is applied until immediatelybefore the selection signal Ss is output to the row selection line LL2is a voltage in the range of −50 V to 0 V. The drive voltage Vin forthat element at the time the selection signal Ss is started to besupplied to the row selection line LL2 is thus 0 to 50 V. When thestatus of the element changes from “selected” to “not selected” asdescribed, the drive voltage Vin applied to that element increases at arelatively high rate γ of change.

When the next row selection period Ts elapses, the row selection circuit21 a outputs a selection signal Ss (a voltage gradually increasing from0 V to 50 V at a rate β) to the raw selection line LL3 (not shown) ofthe third row based on the control signal and outputs 0-V non-selectionsignals Sn to the rest of the row selection lines LL. Meanwhile, thesignal supplying circuit 21 c outputs pixel signals Sd corresponding tothe luminance levels of the respective pixels constituted from theelements in the selected third row to the pixel signal lines UL. Such anoperation is repeated every row selection time Ts until all of the rowsare selected. As a result, at a predetermined time point, electrons areaccumulated in the emitter sections of all the elements in amounts(including zero) corresponding to the luminance levels of the respectiveelements. This summarizes the operation that takes place during thecharge accumulation period Td.

In order to start the emission period Th, the row selection circuit 21 aapplies a large negative voltage (the difference, i.e., −350 V, betweenthe +50 V generated by the power circuit 110 and −400 V generated by thepulse generator 21 b) to all of the row selection lines LL. Here, therow selection circuit 21 a applies a voltage gradually decreasing to−350 V at a rate α of change to every row selection line LL. As aresult, the potential of the lower electrode 12 of each elementgradually changes toward the large negative voltage (−350 V). Meanwhile,the signal supplying circuit 21 c outputs the reference voltage (0 V),which is generated by the pulse generating circuit 21 c 1 and suppliedthrough the amplitude modulator circuit 21 c 2, to all of the pixelsignal lines UL without modulation. The potential of the upperelectrodes 14 of all the elements becomes the reference voltage (0 V).

Consequently, the drive voltage Vin applied to every element graduallychanges toward the second voltage Vp (350 V), which is the positivepredetermined voltage, at a rate a of change. Thus, polarizationreversal occurs again and electrons accumulated in the emitter section13 of each element are simultaneously emitted by Coulomb repulsion. Thiscauses the phosphors above the elements to emit light and to therebydisplay images. Note that the emitter section of the element to which azero drive voltage Vin is applied during the charge accumulation periodTd does not have accumulated electrons and thus no polarization reversaloccurs in this element. Thus, no polarization reversal occurs even whenthe interelectrode voltage (drive voltage) Vin is turned to a largepositive voltage. Thus, for example, the element that is not required toemit light for the purpose of producing a particular image at aparticular timing does not consume excess energy that accompanies thepolarization reversal.

As is described above, during the charge accumulation period Td, thedrive voltage applying circuit 21 consecutively sets the drive voltageVin for the plurality of elements toward the first voltage (the negativepredetermined voltage) Vm one after next. Upon completion of electronaccumulation in all the elements, the drive voltage applying circuit 21simultaneously sets the drive voltage Vin for all the elements at thepositive predetermined voltage Vp so as to cause simultaneous electronemission from all of the elements to initiate the emission period Th.After the predetermined emission period Th has elapsed, the drivevoltage applying circuit 21 again starts the charge accumulation periodTd.

It should be noted that the rates α and β of change in voltage describedabove are each set to a value smaller than the rate γ of change involtage. Thus, light emission due to unnecessary or excessive electronemission during the emission period Th can be avoided, and lightemission due to unnecessary or excessive electron emission during theelectron accumulation period Td can be avoided.

When the charge accumulation period Td is resumed after the emissionperiod Th, the drive voltage Vin applied to each element may be rapidlydecreased from the second voltage Vp to a third voltage Vn (which is avoltage between the first voltage Vm and the second voltage Vp) thatdoes not cause electron accumulation in any element at a rate γ ofchange and may be maintained at the third voltage Vn for a predeterminedperiod before the operation for the charge accumulation period Td isresumed.

In this circuit example, since a predetermined voltage (Vs) is appliedto each focusing electrode, the electrons emitted from the upperelectrode 14 only reach the phosphor directly above the upper electrode14. Thus, a sharp image can be produced.

The collector voltage applying circuit 23 turns off the collectorelectrode 18 at a particular time point between “the time point at whichelectron emission from all of the elements is substantially completedfirst” and “the time point at which the drive voltage Vin of the elementin which the electrons are accumulated fastest starts to decrease towardthe first voltage Vm”. By this operation, the collector electrode 18 isturned off before the charge accumulation period Td of all the elementsis started.

The collector voltage applying circuit 23 turns on the collectorelectrode 18 at a particular time “after the electron accumulation Iscompleted in the element in which the drive voltage Vin is changed tothe first voltage Vm the latest among the elements during the chargeaccumulation period Td” and “before the next substantial completion ofelectron emission from all of the elements”.

As described above, in this electron emitting apparatus 10, no elementaccumulates electrons when other elements are emitting electrons. Thus,the electron emitting apparatus 10 having the plurality of elements cansuppress unnecessary electron emission and impart energy to electronsnormally (properly) emitted merely by switching between the ON statusand the OFF status of the collector electrode 18 using the collectorvoltage applying circuit 23. Thus, the collector voltage applyingcircuit 23 becomes less expensive and simpler.

Second Embodiment

An electron-emitting apparatus according to a second embodiment of thepresent invention will now be described. The second embodiment differsfrom the first embodiment only in that the drive voltage Vin(interelectrode voltage) is changed in a different manner from that inthe electron-emitting apparatus 10 of the first embodiment. Thedescription below mainly concerns this difference.

The drive voltage applying circuit 21 of the second embodiment has anelement voltage measuring circuit, a first detector circuit fordetecting completion of positive-side polarization reversal, and asecond detector circuit for detecting completion of negative-sidepolarization reversal, although these components are not shown in thedrawing. The element voltage measuring circuit monitors the elementvoltage Vka.

The first detector circuit for detecting the completion of thepositive-side polarization reversal monitors the waveform of the elementvoltage Vka measured with the element voltage measuring circuit anddetects, as the time point at which the positive-side polarizationreversal is completed, a time point at which the rate of change Inelement voltage Vka over time (i.e., dVka/dt) starts to increase rapidly(i.e., dVka/dt exceeds the predetermined value) after the rate of changein element voltage Vka over time (i.e., dVka/dt) becomes smaller than apredetermined value when the element voltage Vka reaches the voltagearound the positive coercive field voltage Vd.

Similarly, the second detector circuit for detecting the completion ofthe negative-side polarization reversal monitors the waveform of theelement voltage Vka measured with the element voltage measuring circuit,and detects, as the time point at which the negative-side polarizationreversal is completed, a time point at which the absolute value of therate of change in element voltage Vka over time, i.e., |dVka/dt|, startsto increas rapidly after the absolute value of the rate of change inelement voltage Vka over time, i.e., |dVka/dt| becomes smaller than apredetermined value when the element voltage Vka becomes around thenegative coercive field voltage.

Referring to FIG. 24, during the period (voltage increasing period)between the time t1 at which the voltage is started to Increase and thetime t4 at which the drive voltage Vin reaches the second voltage Vp,which is the positive predetermined voltage, the drive voltage applyingcircuit 21 (in particular, the power supply 21 s) gradually increasesthe drive voltage Vin from the first voltage Vm, which is the negativepredetermined voltage. In this period, the power supply 21 s generatesthe drive voltage Vin that gradually increases from the time t1 (thestart of voltage increase) at a rate (inclination) αS1 of change involtage. When the completion of the positive-side polarization reversal(the time t3) is detected with the first detector circuit, the powersupply 21 s generates the drive voltage Vin gradually increasing at arate (inclination) αL1 of change in voltage which is larger than αS1toward the second voltage Vp from the time t3 to the time t4 at whichthe drive voltage Vin reaces the positive predetermined voltage.

By this operation, within the voltage increasing period (the time t1 totime t4), the drive voltage Vin shows the slowest increase from the timet1 (start of voltage increase) to the time t3 (completion of thepositive-side polarization reversal).

During the period from the time t1 at which the drive voltage Vin isstarted to increase and the time t3 at which the polarization reversalin the emitter section 13 is substantially completed, the inrush currentcaused by the change in drive voltage Vin reaches the maximum. Thus, asin this embodiment, when the drive voltage Vin is increased most slowlyfrom the time t1 (start of voltage increase) to the time t3 (completionof the positive-side polarization reversal), the inrush current flowingin the emitter section 13 can be effectively reduced. Thus, unnecessaryelectron emission due to the inrush current can be avoided. From thetime t3 (completion of the positive-side polarization reversal) to thetime t4 at which the drive voltage Vin reaches the predeterminedpositive voltage, the drive voltage Vin Is gradually increased at arelatively high rate αL1 of change. Thus, the entire length of thevoltage increasing period (the period in which a voltage operation toemit electrons is carried out) can be decreased.

Furthermore, as seen in FIG. 24, the drive voltage applying circuit 21(the power supply 21 s) generates the drive voltage Vin graduallydecreasing from the positive predetermined voltage, i.e., the secondvoltage Vp during the period (voltage decreasing period) from the timet5 at which the voltage starts to decrease to the time t8 at which thedrive voltage Vin reaches a target negative voltage, i.e., the firstvoltage Vm. Here, the power supply 21 s generates the drive voltage Vingradually decreasing at a rate (inclination) βs1 (βs1>0) of change fromthe time t5. When the completion of the negative-side polarizationreversal is detected with the second detector circuit at the time t7,the power supply 21 s generates the drive voltage Vin graduallydecreasing toward the first voltage Vm at a rate βL1 (βL1>0) of changewhich is larger than βS1 until the time t8 at which the the drivevoltage Vin reaches the target negative voltage.

By this operation, in the drive voltage Vin decreasing period (t5 tot8), the drive voltage Vin shows the slowest decrease between the timet5 at which the voltage starts to decrease till the time t7 at which thenegative-side polarization reversal is completed.

During the period from the time t5 at which the drive voltage Vin startsto decrease to the time t7 at which the negative-side polarizationreversal in the emitter section 13 is substantially completed, theinrush current due to the change in drive voltage Vin reaches themaximum. Thus, as in this embodiment, by decreasing the drive voltageVin most slowly from the time t5 (start of voltage decrease) to the timet7 (completion of the negative-side polarization reversal), the inrushcurrent flowing in the emitter section 13 can be effectively reduced. Asa result, unnecessary electron emission due to inrush current can beavoided. From the time t7 at which the negative-side polarizationreversal is completed to the time t8 at which the drive voltage Vinreaches the target negative voltage, the drive voltage Vin is graduallydecreases at a relatively high rate βL1 of change. Thus, the entirelength of the voltage decreasing period (the period in which a voltageoperation to accumulate electrons) can be reduced.

Third Embodiment

An electron-emitting apparatus according to a third embodiment of thepresent invention will now be described. The third embodiment differsfrom the second embodiment only in the manner the drive voltage Vin(interelectrode voltage) is changed. The description below mainlyconcerns this difference.

In the third embodiment, the power supply 21 s of the drive voltageapplying circuit 21 generates the voltage indicated in FIG. 25, and thedrive voltage applying circuit 21 applies this voltage functioning asthe drive voltage Vin between the upper electrode 14 and the lowerelectrode 12.

In detail, referring to FIG. 25, the drive voltage applying circuit 21(power supply 21 s) gradually increases the drive voltage Vin from thefirst voltage Vm, i.e., the negative predetermined voltage, during theperiod (voltage increasing period) from the time t1 at which the voltagestarts to increase to the time t4 at which the drive voltage Vin reachesthe positive predetermined voltage, i.e., the second voltage Vp. Fromthe time t1, the power supply 21 s generates the drive voltage Vingradually increasing at a rate (inclination) αL2. When the completion ofthe positive-side polarization reversal (i.e., the time t3) is detectedwith the first detector circuit, the power supply 21 s generates thedrive voltage Vin gradually increasing toward the second voltage Vp at arate αS2 which is smaller than αL2 until the time t4 at which the drivevoltage Vin reaches the positive predetermined voltage.

By this operation, within the voltage increasing period (t1 to t4), thedrive voltage Vin shows the slowest increase from the time t3 at whichthe positive-side polarization reversal is completed to the time t4 atwhich the positive predetermined voltage is reached.

In some elements by themselves or other elements with some measures toavoid unnecessary electron emission, unnecessary electron emission dueto a rapid change in element voltage Vka upon completion of thepositive-side polarization reversal occurs more frequently than theunnecessary electron emission due to the inrush current that occurs atthe start of increasing the interelectrode voltage (drive voltage) Vin.Thus, as in this embodiment, when the rate of increase in the drivevoltage Vin is adjusted to be lowest from the time t3 (completion of thepositive-side polarization reversal) to the time t4 (reaching thepredetermined positive voltage), unnecessary electron emission can beeffectively avoided. From the time t1 (start of the voltage increase) tothe time t3 (completion of the positive-side polarization reversal), thedrive voltage Vin can be gradually increased at a relatively high rateαL2. Thus, the entire length of the voltage increasing period (theperiod in which a voltage operation to emit electrons is carried out)can be reduced as a whole.

Again referring to FIG. 25, the drive voltage applying circuit 21 (powersupply 21 s) generates the drive voltage Vin gradually decreasing fromthe second voltage Vp (positive predetermined voltage) during the period(voltage decreasing period) from the time t5 at which the voltage startsto decrease till the time t8 at which the drive voltage Vin reaches thefirst voltage Vm, which is the target negative voltage. From the time t5at which the voltage starts to decrease, the power supply 21 s generatesthe drive voltage Vin gradually decreasing at a rate (inclination) βL2(βL2>0). When the completion of the negative-side polarization reversalis detected with the second detector circuit (the time t7), the powersupply 21 s generates the drive voltage Vin gradually decreasing towardthe first voltage Vm at a rate βS2 (βS2>0) smaller than βL2 until thetime t8 at which the drive voltage Vin reaches the target negativevoltage.

By this operation, within the voltage decreasing period (the time t5 tothe time t8), the drive voltage Vin is decreased at the lowest rateduring the period from the time t7 at which the negative-sidepolarization reversal is completed to the time t8 at which the drivevoltage Vin reaches the target negative voltage.

In some elements by themselves or other elements with some measures toavoid unnecessary electron emission, unnecessary electron emission dueto a rapid change in element voltage Vka upon completion of thenegative-side polarization reversal occurs more frequently than theunnecessary electron emission due to the inrush current that occurs atthe start of decreasing the drive voltage Vin. Thus, by most slowlydecreasing the drive voltage Vin from the time t7 at which thenegative-side polarization reversal is completed till the time t8 atwhich the drive voltage Vin reaches the target negative voltage,unnecessary electron emission can be effectively avoided. Since thedrive voltage Vin is decreased at a relatively high rate βL2 from thetime t5 to the time t7 at which the negative-side polarization reversalis completed, the entire length of the voltage decreasing period (theperiod in which a voltage operation to accumulate electrons) can bereduced.

Fourth Embodiment

An electron-emitting apparatus according to a fourth embodiment of thepresent invention will now be described. The fourth embodiment differsfrom the electron-emitting apparatus 10 of the first embodiment only inthe manner the drive voltage Vin is changed. Thus, the description belowmainly concerns this difference.

In the fourth embodiment, the power supply 21 s of the drive voltageapplying circuit 21 generates the voltage shown in FIG. 26, and thedrive voltage applying circuit 21 applies this voltage as the drivevoltage Vin between the upper electrode 14 and the lower electrode 12.

In detail, referring to FIG. 26, at the time t1, the drive voltageapplying circuit 21 (power supply 21 s) generates the drive voltage Vinrapidly decreasing at a rate (inclination) k1 from the second voltage Vpto the third voltage Vn. Subsequently, the power supply 21 s maintainsthe third voltage Vn, as the drive voltage Vin, from the time t1 untilthe time t2 (a particular time after the time t1) at which the voltageis started to decrease.

The third voltage Vn is an intermediate voltage between the firstvoltage Vm, which is the negative predetermined voltage, and the secondvoltage Vp, which is the positive predetermined voltage, as describedabove. The third voltage Vn is a voltage that does not cause electronaccumulation (or additional electron accumulation) in or electronemission from the emitter section 13 when the element voltage Vka iscoincident with the third voltage Vn.

Subsequently, at the time t2 at which the voltage is started todecrease, the power supply 21 s generates the drive voltage Vindecreasing from the third voltage Vn at a rate k2 of change. At the timet3, which is presumably the time that the negative-side polarizationreversal is completed and is a predetermined time after the time t2, thepower supply 21 s generates the drive voltage Vin decreasing from thedrive voltage Vin at the time t3 at a rate k3 of change until the timet4 at which the drive voltage Vin reaches the target negative voltage,i.e., the first voltage Vm.

From the time t4 to the time t5, the power supply 21 s maintains thedrive voltage Vin at the first voltage Vm. At the time t5, the powersupply 21 s generates the drive voltage Vin rapidly increasing from thefirst voltage Vm to the third voltage Vn at a rate (inclination) k4 ofchange. Subsequently, the power supply 21 s maintains the third voltageVn from the time t5 to the time t6, which is a predetermined time afterthe time t5 and which is a time point at which the voltage is started toincrease.

At the time t6 at which the voltage starts to increase, the power supply21 s generates the drive voltage Vin Increasing from the third voltageVn at a rate k5. At the time t7 which is a predetermined time after thetime t6 (start of voltage increase) and is presumably the time at whichthe positive-side polarization reversal is completed, the power supply21 s generates the drive voltage Vin increasing from the voltage levelat the time t7 at a rate K6 of change until the drive voltage Vinreaches the second voltage Vp at the time t8. Thereafter, the powersupply 21 s repeats generation of voltages at the time t1 to the timet8.

In this embodiment, the relationship k3<k2<k1 is set. That is, after thepower supply 21 s generates the second voltage Vp, the power supply 21 sgenerates a voltage decreasing from the second voltage Vp toward thethird voltage Vn at the time ti so that the voltage is maintained at alevel that does not cause electron accumulation or electron emission inor from the emitter section 13, the voltage level being between thenegative predetermined voltage and the positive predetermined voltagedescribed above. Subsequently, from the time t2 to the time t4, thepower supply 21 s generates the voltage which decreases from the thirdvoltage Vn toward the first voltage Vm more slowly compared with thedecrease in voltage from the second voltage Vp to the third voltage Vnwhich takes place at the time t1. According to an experiment, the rapidchange in drive voltage Vin from the second voltage Vp to the thirdvoltage Vn did not cause unnecessary electron emission. Thus, accordingto this embodiment, the drive voltage Vin that changes slowly from thethird voltage Vn to the first voltage Vm is applied to the element.Therefore, unnecessary electron emission can be avoided while reducingthe entire time required for the electron accumulation after theelectron emission.

Furthermore, in this embodiment, the relationship k6<k5<k4 is set. Inother words, after the power supply 21 s generates the first voltage Vm,the power supply 21 s generates the voltage increasing from the firstvoltage Vm to the third voltage Vn so that the voltage is maintained ata level that does not cause electron accumulation in or electronemission from the emitter section 13, the voltage level being betweenthe negative predetermined voltage and the positive predeterminedvoltage described above. Subsequently, the power supply 21 s generatesthe voltage which increases from the third voltage Vn to the secondvoltage Vp more slowly compared with the increase in voltage from thefirst voltage Vm to the third voltage Vn (time t6). According to anexperiment, the rapid change in drive voltage Vin from the first voltageVm to the third voltage Vn did not cause unnecessary electron emission.Moreover, in this embodiment, the drive voltage Vin slowly changing fromthe third voltage Vn to the second voltage Vp is applied to the element.Thus, unnecessary electron emission can be avoided while reducing theentire time required for the electron emission after the electronaccumulation.

It is to be understood that the relationship k2≦k3≦k1 or k5≦k6<k4 may bealternatively used. That is, the relationships between k2 and k3 andbetween k5 and k6 can be suitably determined based on the properties ofthe element, e.g., at which point of time the unnecessary electronemission takes place.

Alternatively, as with the embodiments afore-mentioned, the elementvoltage Vka may be monitored, the time t3 at which the negative-sidepolarization reversal is completed may be detected when the elementvoltage Vka is below the voltage corresponding to the negative coercivefield voltage, and/or the time t7 at which the positive-sidepolarization reversal is completed may be detected when the elementvoltage Vka is above the voltage corresponding the positive coercivefield voltage so that the rates of change in drive voltage Vin at therespective time points may be adjusted as described above.

Fifth Embodiment

An electron-emitting apparatus according to a fifth embodiment of thepresent invention will now be described. The fifth embodiment differsfrom the fourth embodiment only in that the drive voltage Vin of theelectron-emitting apparatus is changed stepwise. Thus, the descriptionbelow mainly concerns this difference.

Referring to FIG. 27, an electron-emitting apparatus 30 of the fifthembodiment includes an element D and a drive voltage applying circuit31. The element D is the same as the element in the first embodiment. Inthe drawing, the transparent plate 17, the collector electrode 18, andthe phosphor 19 are omitted. The lower electrode 12 of the element D isearthed.

The drive voltage applying circuit 31 has a voltage control circuit 32,a switching circuit 33, a plurality of resistors 34 a to 34 g, and aplurality of constant voltage sources 35 a to 35 g.

The voltage control circuit 32 is connected to the lower electrode 12and the upper electrode 14 of the element D and the switching circuit33. The voltage control circuit 32 measures the element voltage Vka andsends a switching signal to the switching circuit 33 based on theobserved (measured) element voltage Vka.

The switching circuit 33 has a fixed connection point ks connected tothe upper electrode 14 of the element D and a plurality of (in thisembodiment, seven) connecting points 33 a to 33 g for voltageapplication. The switching circuit 33 selects one of the connectingpoints 33 a to 33 g in response to the switching signal fed from thevoltage control circuit 32, and connects the fixed connection point ksto the selected connecting point for voltage application.

The connecting point 33 a is connected to a first end of the resistor 34a. A second end of the resistor 34 a is connected to the cathode of theconstant voltage source 35 a generating a voltage |Vm| (the same voltageas the first voltage Vm). The anode of the constant voltage source 35 ais earthed. The connecting point 33 b is connected to a first end of theresistor 34 b. A second end of the resistor 34 b is connected to thecathode of the constant voltage source 35 b generating a voltage |V1|.The anode of the constant voltage source 35 b is earthed. The connectingpoint 33 c is connected to a first end of the resistor 34 c. A secondend of the resistor 34 c is connected to the cathode of the constantvoltage source 35 c generating a voltage |V2|. The anode of the constantvoltage source 35 c is earthed. The relationship |V1|<|V2|<|Vm| (Vm<0)is established here.

The connecting point 33 d is connected to a first end of the resistor 34d. A second end of the resistor 34 d is connected to the anode of theconstant voltage source 35 d generating the third voltage Vn describedabove. The cathode of the constant voltage source 35 d is earthed. Theconnecting point 33 e is connected to a first end of the resistor 34 e.A second end of the resistor 34 e is connected to the anode of theconstant voltage source 35 e generating a voltage V3. The cathode of theconstant voltage source 35 e is earthed. The connecting point 33 f isconnected to a first end of the resistor 34 f. A second end of theresistor 34 f is connected to the anode of the constant voltage source35 f generating a voltage V4. The cathode of the constant voltage source35 f is earthed. The connecting point 33 g is connected to a first endof the resistor 34 g. A second end of the resistor 34 g is connected tothe anode of the constant voltage source 35 g generating the secondvoltage Vp described above. The cathode of the constant voltage source35 g is earthed. The relationship 0<Vn<V3<V4 <Vp is established here.

The operation of the drive voltage applying circuit 31 having theabove-described configuration will now be described with reference toFIG. 28. Assume that before the time t1, the switching circuit 33connects the fixed connection point ks to the connecting point 33 g forvoltage application and thus, the second voltage Vp (Vp>0) is applied tothe element D. At the time t1, the voltage control circuit 32 sends aswitching signal to the switching circuit 33, and the switching circuit33 connects the fixed connection point ks to the connecting point 33 din response to this signal. As a result, the drive voltage applyingcircuit 31 generates the third voltage Vn as the drive voltage Vin. Inother words, at the time t1, the drive voltage Vin decreases from thesecond voltage Vp to the third voltage Vn at a relatively high rate ofchange in voltage.

After a predetermined time after the time t1, the voltage controlcircuit 32 sends a switching signal to the switching circuit 33, and theswitching circuit 33 connects the fixed connection point ks to theconnecting point 33 b in response to the signal at the time t2. As aresult, the drive voltage applying circuit 31 generates the voltage V1(V1<0) as the drive voltage Vin. Subsequently, the voltage controlcircuit 32 monitors the element voltage Vka, assumes (detects)completion of the negative-side polarization reversal when the elementvoltage Vka is below the negative coercive field voltage, and sends aswitching signal to the switching circuit 33, when the completion of thenegative-side polarization reversal is detected. In response to thissignal, the switching circuit 33 connects the fixed connection point ksto the connecting point 33 c. The drive voltage applying circuit 31 thusgenerates the voltage V2 (V2<0) as the drive voltage Vin at the time t3.

A predetermined time after the time t3, i.e., at the time t4, thevoltage control circuit 32 sends a switching signal to the switchingcircuit 33, and the switching circuit 33 connects the fixed connectionpoint ks to the connecting point 33 a in response to this signal. As aresult, the drive voltage applying circuit 31 generates the firstvoltage Vm (Vm<0) as the drive voltage Vin. After a predetermined timefrom the time t4 and until the time t5, the drive voltage applyingcircuit 31 continues generation of the first voltage Vm as the drivevoltage Vin. The element voltage Vka thus reaches the negativepredetermined voltage in the period from the time t2 to the time t5. Inother words, the electron accumulation in the emitter section 13 iscompleted within this period.

At the time t5, the voltage control circuit 32 sends a switching signalto the switching circuit 33, and the switching circuit 33 connects thefixed connection point ks to the connecting point 33 d in response tothis signal. The drive voltage applying circuit 31 thus generates thethird voltage Vn (Vn>0) as the drive voltage Vin. That is, at the timet5, the drive voltage Vin changes from the first voltage Vm to the thirdvoltage Vn at a relatively high rate of change in voltage.

After a predetermined time from the time t5, at the time t6, the voltagecontrol circuit 32 sends a switching signal to the switching circuit 33,and the switching circuit 33 connects the fixed connection point ks tothe connecting point 33 e in response to this signal. The drive voltageapplying circuit 31 thus generates the voltage V3 (V3>0) as the drivevoltage Vin. Subsequently, the voltage control circuit 32 monitors theelement voltage Vka, assumes (detects) completion of the positive-sidepolarization reversal when the element voltage Vka is above the positivecoercive field voltage, and sends a switching signal to the switchingcircuit 33 when the completion of the positive-side polarizationreversal is detected. The switching circuit 33 connects the fixedconnection point ks to the connecting point 33 f in response to thissignal. The drive voltage applying circuit 31 thus generates the voltageV4 (V4>0) as the drive voltage Vin at the time t7.

After a predetermined time from the time t7, at the time t8, the voltagecontrol circuit 32 sends a switching signal to the switching circuit 33,and the switching circuit 33 connects the fixed connection point ks tothe connecting point 33 g in response to this signal. The drive voltageapplying circuit 31 thus generates the second voltage Vp as the drivevoltage Vin again. The drive voltage applying circuit 31 repeats thegeneration of the voltages at the time t1 to the time t8 from here on.

In the fifth embodiment, the constant voltage sources 35 a to 35 g andthe switching circuit 33 functions as if they form one power supply.Thus, as with the power supply 21 s of the fourth embodiment, the powersupply of the fifth embodiment generates the second voltage Vp, and, atthe subsequent time t1, generates a voltage decreasing from the secondvoltage Vp to the third voltage Vn so that the voltage is maintained atthe level that does not cause electron accumulation or electron emissionin or from the emitter section 13, the voltage level being between thenegative predetermined voltage and the positive predetermined voltagedescribed above. Moreover, from the time t2 to the time t4, the powersupply generates a voltage (a voltage gradually decreasing to the firstvoltage Vm) that slowly decreases from the third voltage Vn toward thefirst voltage Vm when compared with the decrease from the second voltageVp to the third voltage Vn that takes place at the time t1. Moreover,upon completion of the negative-side polarization reversal, the drivevoltage Vin is gradually decreased. Thus, as with the fourth embodiment,the electron-emitting apparatus 30 of the fifth embodiment can avoidunnecessary electron emission during the electron accumulation and canreduce the time required for the electron accumulation from after theelectron emission.

As with the power supply 21 s of the fourth embodiment, the power supplyof this embodiment generates the first voltage Vm, and then generates avoltage increasing from the first voltage Vm to the third voltage Vn sothat the voltage Is maintained at a level that does not cause electronaccumulation in or electron emission from the emitter section 13, thevoltage level being between the negative predetermined voltage and thepositive predetermined voltage described above. Subsequently, from thetime t6 to the time t8, the power supply generates a voltage graduallyand slowly increasing from the third voltage Vn to the second voltage Vpwhen compared with the increase from the first voltage Vm to the thirdvoltage Vn (the time t5). In addition, the drive voltage Vin increasesslowly also after the completion of the positive-side polarizationreversal. Thus, the electron-emitting apparatus 30 can avoid unnecessaryelectron emission during the electron emission and reduce the timerequired for the electron emission from after the electron accumulation.

According to this embodiment, the power supply for generating drivevoltage Vin that can avoid unnecessary electron emission can be providedby the above-described simple configuration of switching the constantvoltage source using the switching circuit 33. With this drive voltageapplying circuit 31, a simple power supply that can generate desireddrive voltages Vin can be provided even when the properties of theelements are varied or even when the desired drive voltage Vin requiredfor electron emission and accumulation changes with the change in thenumber of elements from which emission is required in theelectron-emitting apparatus. Besides, since the element voltage Vka ismonitored and the level of the drive voltage Vin is switched when theelement voltage Vka is below the negative coercive field voltage orabove the positive coercive field voltage, an appropriate level of thedrive voltage Vin can be applied to the element at an appropriate timingeven when the element voltage Vka is changed with changes in propertiesof the element or in number of the electrons emitted.

The resistances of the resistors 34 a to 34 g may be the same ordifferent. The advantages of setting the resistances of the resistors 34a to 34 g at appropriate levels (changing the circuit parameter) will bedescribed below in the seventh embodiment. Note that in the fifthembodiment, seven constant voltage sources are provided. However, thenumber of the pairs of the constant voltage sources and the resistorsmay be lager so that the drive voltage Vin can be generated stepwisewith a smaller step difference.

Sixth Embodiment

An electron-emitting apparatus according to a sixth embodiment of thepresent invention will now be described. The sixth embodiment differsfrom the electron-emitting apparatus 10 of the first embodiment only inthe manner in which the drive voltage (interelectrode voltage) Vin ischanged. Thus, the description below mainly concerns this difference.

The drive voltage supplying circuit of the sixth embodiment has theelement voltage measuring circuit and the second detector circuit fordetecting the completion of the negative-side polarization reversal (notshown) included in the drive voltage applying circuit 21 of the secondembodiment.

Referring to FIG. 29, as with the drive voltage applying circuit 21 ofthe first embodiment, the drive voltage applying circuit (power supply)generates the drive voltage Vin gradually increasing from the firstvoltage Vm (the negative predetermined voltage) to the second voltage Vp(the positive predetermined voltage) during the period (voltageincreasing period) from the time t1 at which the voltage starts toincrease to the time t2 at which the drive voltage Vin reaches thesecond voltage Vp. The drive voltage applying circuit also generates adrive voltage Vin gradually decreasing from the second voltage Vp to thefirst voltage Vm during the period (voltage decreasing period) from thetime t3 at which the voltage is started to decrease to the time t4 atwhich the drive voltage Vin reaches the first voltage Vm. The drivevoltage Vin to be reached at the time t4 is also referred to as the“fourth voltage” for the convenience sake.

When the second detector circuit detects the completion of thenegative-side polarization reversal (the time t5) after the time t4, thedrive voltage applying circuit rapidly increases the drive voltage Vinfrom the first voltage Vm to a fifth voltage at a rate α of change involtage, and then gradually decreases the drive voltage toward thenegative first voltage Vm at a rate β of change in voltage smaller thanthe rate α. Here, the absolute value of the first voltage (fourthvoltage) Vm is larger than the absolute value of the fifth voltage. Inother words, at the time the negative-side polarization reversal issubstantially completed in the emitter section 13, the drive voltage Vinis caused to become a voltage near the element voltage Vka at this timepoint, i.e., the drive voltage Vin is controlled to a value near thenegative coercive field voltage. Subsequently, the drive voltageapplying circuit 21 gradually decreases the drive voltage Vin toward thefirst voltage Vm so that the drive voltage Vin reaches the first voltageVm at the time t6. The rate of change in voltage during this period(from the time t5 to the time t6) is smaller than that in the periodfrom the time t3 to the time t4 or at the time t5.

At the time t7 after the time t6, the drive voltage applying circuit 21generates a voltage that increases the drive voltage Vin. After thistime point, the drive voltage applying circuit repeats the generation ofthe voltages at the time t1 to the t7.

According to an experiment, upon completion of the negative-sidepolarization reversal, the element voltage Vka shows a steep change, andunnecessary electron emission is frequently observed. Thus, by changingthe voltage generated by the power supply as in this sixth embodiment,the change in element voltage Vka upon completion of the negative-sidepolarization reversal can be moderated and unnecessary electron emissioncan be effectively avoided. Since the power supply generates the firstvoltage Vm until completion of the negative-side polarization reversal,the length of time from the time t3 at which the voltage starts todecrease to the time t5 at which the negative-side polarization reversalIs completed can be further reduced.

It can be said that the changes in drive voltage Vin after thenegative-side polarization reversal, i.e., after the period from thetime t5 to the time t6, are the same as an operation where the electronsfrom the upper electrode 14 are caused to be accumulated in the emittersection 13 by generating a voltage gradually decreasing toward the firstvoltage Vm so that the element voltage Vka reaches the negativepredetermined value, after the electrons are caused to emitted from theemitter section 13 from the time t1 to the time t3 by changing the drivevoltage Vin toward the second voltage Vp.

In this embodiment, the fourth voltage to be reached at the time t4 isset to the first voltage Vm. However, the fourth voltage is not limitedto the first voltage Vm. The voltage to be reached at the time t4 may beany voltage that can cause negative-side polarization reversal in theemitter section.

In this embodiment, the power supply generates a voltage that changesfrom the fourth voltage to the fifth voltage at the completion of thenegative-side polarization reversal (the time t5) and then graduallydecreases toward the first voltage. Alternatively, the power supply maygenerate a voltage that changes from the fourth voltage to the fifthvoltage after the t4 but before the completion of the negative-sidepolarization reversal (the time t5) and then gradually decreases towardthe first voltage.

In this embodiment, from the time t4 at which the target negativevoltage is reached to the time t5 of completion of the negative-sidepolarization reversal, the power supply generates a constant voltage,i.e., the fourth voltage (the first voltage Vm). Alternatively, thepower supply may generate a voltage that changes in a negative voltagerange whose absolute value Is larger than the absolute value of thefifth voltage. For example, a voltage that gradually changes from thefourth voltage toward the fifth voltage may be generated.

Furthermore, in this embodiment, from the time t3 at which the voltagestarts to decrease to the time t4 at which the target negative voltageis reached, the power supply generates a voltage gradually decreasingtoward the fourth voltage (first voltage Vm). Alternatively, the powersupply may generate a voltage that immediately changes to the fourthvoltage at the time t3.

Seventh Embodiment

An electron-emitting apparatus according to a seventh embodiment of thepresent invention will now be described. The seventh embodiment differsfrom the second embodiment shown in FIG. 24 only in the circuit variousparameters of the circuit for connecting the power supply 21 s to theelement are used. The description below thus mainly concerns thisdifference.

Referring to FIG. 30, an electron-emitting apparatus 40 of the seventhembodiment includes an element D constituted from the lower electrode12, the emitter section 13, and the upper electrode 14; and a drivevoltage applying circuit 41. The element D is the same as the element inthe first embodiment, and the transparent plate 17, the collectorelectrode 18, and the phosphor 19 is omitted from the drawing. The drivevoltage applying circuit 41 includes the drive voltage applying circuit21 described above and a circuit parameter switching circuit (circuitparameter switching means) 42.

The circuit parameter switching circuit 42 is connected in series to(inserted in series into) the circuit for connecting the element D tothe power supply 21 s in the drive voltage applying circuit 21. Thecircuit parameter switching circuit 42 has a switching element 42 a anda plurality of circuit elements (circuit parameter setting elements) 42b 1, 42 b 2, 42 b 3, and 42 b 4.

The switching element 42 a receives a control signal from the drivevoltage applying circuit 21, and selectively connects the fixedconnection point connected to the upper electrode 14 of the element D toone of the connecting points connected to the circuit elements 42 b 1,42 b 2, 42 b 3, and 42 b 4 so that one of the circuit elements 42 b 1,42 b 2, 42 b 3, and 42 b 4 is connected in series in (inserted in seriesinto) the circuit. The circuit elements 42 b 1, 42 b 2, 42 b 3, and 42 b4 have different resistances (resistance values).

Next, the operation of the electron-emitting apparatus 40 having theabove-described structure is explained. As is previously stated, theelectron-emitting apparatus 40 changes the drive voltage Vin in the samemanner as the electron-emitting apparatus of the second embodiment.

Now, referring to FIG. 31, in the electron-emitting apparatus 40, theswitching element 42 a connects the circuit element 42 b 1 to (insertsthe circuit element.42 b 1 in series into) the circuit during a periodTA1 from the time t4 (the time at which the target positive voltage isreached) or the time tx1 (the time immediately after electron emissionis substantially completed) Immediately after the time t4, to the timet7 at which the negative-side polarization reversal is completed.

The electron-emitting apparatus 40 then connects the circuit element 42b 2 to the circuit using the switching element 42 a during a period TA2from the time t7 at which the negative-side polarization reversal iscompleted to the time t8 at which the target negative voltage is reachedor the time ty2 immediately after the completion of the electronaccumulation which comes after the time t8.

The electron-emitting apparatus 40 then connects the circuit element 42b 3 to (inserts the circuit element 42 b 3 in series into) the circuitusing the switching element 42 a during a period TA3 from the time ofcompletion of the electron accumulation (i.e., the time ty2 and the timety1 in FIG. 31 since the waveform of the drive voltage Vin is repeated)to the time of completion of the next positive-side polarizationreversal (the time t3).

The electron-emitting apparatus 40 then connects the circuit element 42b 4 to (inserts the circuit element 42 b 4 in series into) the circuitusing the switching element 42 a during a period TA4 from the completionof the positive-side polarization reversal (the time t3) to thecompletion of the electron emission (the time tx1). Theelectron-emitting apparatus 40 repeats the selecting and connecting ofthe circuit elements as described above.

In this manner, at least two (in this embodiment, all four) of thefollowing circuit elements are different from each other:

a circuit element connected to (inserted in series into) the circuitduring a first period TB1 from the time t5 to the time t7, the time t5being the time at which generation of the voltage (drive voltage Vin)decreasing toward the first voltage Vm is started and the time t7 beingthe time at which the polarization reversal (the negative-sidepolarization reversal) in the emitter section 13 is substantiallycompleted while the voltage is decreased;

a circuit element connected to (inserted in series into) the circuitduring a second period TB2 from the time t7 to the time of completion ofthe electron accumulation between the time t8 to the time ty2, the timet7 being the time of completion of the negative-side polarizationreversal;

a circuit element connected to (inserted in series into) the circuitduring a third period TB3 from the time t1 to the time t3, the time t1being the time at which generation of the voltage increasing toward thesecond voltage Vp is started and the time t3 being the time at which thepositive-side polarization reversal In the emitter section 13 issubstantially completed while the voltage is increased; and

a circuit element connected to (inserted in series into) the circuitduring a fourth period TB4 from the time t3 of completion of thepositive-side polarization reversal to the time at which the electronemission from the emitter section 13 is substantially completed betweenthe time t4 to the time tx1.

In this embodiment, the circuit element (e.g., a resistor) connected tothe circuit is selected for each period so that the circuit parameterduring the period in which unnecessary electron emission is frequent dueto the properties of the emitter section 13 of the element D differsfrom the circuit parameters during other periods. As a result, whencompared with cases in which the circuit parameter is not changed, thetime from the start of the electron accumulation to the completion ofelectron emission can be reduced while avoiding unnecessary electronemission.

In this embodiment, the drive voltage Vin is changed gradually.Alternatively, as shown in FIGS. 26 and 28, the drive voltage Vin may bea voltage that maintains the third voltage Vn for a particular length oftime when the voltage is changing from the first voltage Vm to thesecond voltage Vp or vise versa. Alternatively, as shown in FIG. 41, thedrive voltage Vin may be rectangular waves.

In this embodiment, the circuit elements 42 b 1, 42 b 2, 42 b 3, and 42b 4 are resistors having different resistances. However, it issufficient if at least two of these circuit elements have resistancesdifferent from each other. Moreover, the circuit elements may include,other than resistors, coils and capacitors. In such a case, at least twoof the circuit elements 42 b 1, 42 b 2, 42 b 3, and 42 b 4 should haveimpedances Z different from each other.

Eighth Embodiment

An electron-emitting apparatus 50 according to an eighth embodiment ofthe present invention will now be described with reference to FIG. 32.The electron-emitting apparatus 50 differs from the electron-emittingapparatus 10 only in that the collector electrode 18 and the phosphors19 of the electron-emitting apparatus 10 are replaced with a collectorelectrode 18′ and phosphors 19′. Thus, the description below mainlyconcerns this difference.

In the electron-emitting apparatus 50, a phosphor 19′ is disposed on theback surface (the surface facing the upper electrode 14) of thetransparent plate 17, and a collector electrode 18′ is disposed to coverthe phosphor 19′. The collector electrode 18′ has a thickness thatallows electrons emitted from the emitter section 13 through the microthrough holes 14 a in the upper electrode 14 to travel through(penetrate) the collector electrode 18′. The thickness of the collectorelectrode 18′ is preferably 100 nm or less. The thickness of thecollector electrode 18′ can be larger as the kinetic energy of theemitted electrons is higher.

The configuration of this embodiment is typically employed in cathoderay tubes (CRTs). The collector electrode 18′ functions as a metal back.The electrons emitted from the emitter section 13 through the microthrough holes 14 a in the upper electrode 14 travel through thecollector electrode 18′, enter the phosphor 19′, and excites thephosphor 19′, thereby allowing light emission. The advantages of theelectron-emitting apparatus 50 are as follows:

(a) When the phosphor 19′ is not electrically conductive,electrification (negative charging) of the phosphor 19′ can be avoided.Thus, the electric field that accelerates electrons can be maintained.

(b) Since the collector electrode 18′ reflects light generated by thephosphor 19′, the light can be emitted toward the transparent plate 17side (the emission surface side) with higher efficiency.

(c) Since collision of excessive electrons on the phosphor 19′ can beavoided, deterioration of the phosphor 19′ and the generation of gasfrom the phosphor 19′ can be avoided.

Materials of Constituent Components and Production Examples

The materials of the constituent components of the individualelectron-emitting apparatuses described above and the method forproducing the constituent components will now be described.

Lower Electrode 12

The lower electrode is composed of an electrically conductive materialas described above. Examples of the preferable materials for the lowerelectrode are as follows:

(1) Conductors resistant to high-temperature oxidizing atmosphere (e.g.,elemental metals or alloys)

Examples: high-melting-point noble metals such as platinum, iridium,palladium, rhodium, and molybdenum

Examples: materials mainly composed of a silver-palladium alloy, asilver-platinum alloy, or a platinum-palladium alloy

(2) Mixtures of ceramics having electrical isolation and being resistantto high-temperature oxidizing atmosphere and elemental metals

Example: a cermet material of platinum and a ceramic

(3) Mixtures of ceramics having electrical isolation and being resistantto high-temperature oxidizing atmosphere and alloys

(4) Carbon-based or graphite-based materials

Of these, elemental platinum and materials mainly composed of platinumalloys are particularly preferable. When a ceramic material is added tothe electrode material, it is preferable to use 5 to 30 percent byvolume of the ceramic material. Materials similar to those of the upperelectrode 14 described below are also usable. The lower electrode ispreferably formed by a thick-film forming process. The thickness of thelower electrode is preferably 20 μm or less and most preferably 5 μm orless.

Emitter Section 13

The dielectric material that constitutes the emitter section may be adielectric material having a relatively high relative dielectricconstant (for example, a relative dielectric constant of 1,000 orhigher) or a ferroelectric material. Examples of the preferable materialfor the emitter section are as follows:

(1) Barium titanate, lead zirconate, lead magnesium niobate, lead nickelniobate, lead zinc niobate, lead manganese niobate, lead magnesiumtantalate, lead nickel tantalate, lead antimony stannate, lead titanate,lead magnesium tungstate, and lead cobalt niobate

(2) Ceramics containing any combination of the substances listed in (1)above

(3) Ceramics described in (2) further containing an oxide of lanthanum,calcium, strontium, molybdenum, tungsten, barium, niobium, zinc, nickel,or manganese; ceramics described In (2) further containing anycombination of the oxides described above; and ceramics described in (2)further containing other compounds

(4) Materials mainly containing 50% or more of the materials listed in(1) above

It Is noted that, for example, a two-component system containing leadmagnesium niobate (PMN) and lead titanate (PT), i.e., nPMN-mPT (n and mrepresent molar ratios), can exhibit a decreased Curie point and a largerelative dielectric constant at room temperature by increasing the molarratio of the PMN. In particular, nPMN-mPT having n of 0.85 to 1.0 and mof 1.0-n exhibits a relative dielectric constant of 3,000 or higher andis thus particularly preferable as the material for the emitter section.For example, the nPMN-mPT having n of 0.91 and m of 0.09 exhibits arelative dielectric constant of 15,000 at room temperature. The nPMN-mPThaving n of 0.95 and m of 0.05 exhibits a relative dielectric constantof 20,000 at room temperature.

Furthermore, a three-component system containing lead magnesium niobate(PMN), lead titanate (PT), and lead zirconate (PZ), i.e., PMN-PT-PZ, canexhibit a high relative dielectric constant by increasing the molarratio of PMN. In this three-component system, the relative dielectricconstant can be increased by adjusting the composition to near themorphotropic phase boundary (MPB) between the tetragonal and pseudocubicphases or between the tetragonal and rhombohedral phases.

For example, PMN:PT:PZ of 0.375:0.375:0.25 yields a relative dielectricconstant of 5,500, and PMN:PT:PZ of 0.5:0.375:0.125 yields a relativedielectric constant of 4,500. These compositions are particularlypreferable as the material for the emitter section.

Furthermore, a metal, such as platinum, may be added to the dielectricmaterial to improve the dielectric constant so long as the insulatingability can be ensured. For example, 20 percent by weight of platinummay be added to the dielectric material.

A piezoelectric/electrostrictive layer or an antiferroelectric layer maybe used as the emitter section. When the emitter section is apiezoelectric/electrostrictive layer, the piezoelectric/electrostrictivelayer may be composed of a ceramic containing lead zirconate, leadmagnesium niobate, lead nickel niobate, lead zinc niobate, leadmanganese niobate, lead magnesium tantalate, lead nickel tantalate, leadantimony stannate, lead titanate, barium titanate, lead magnesiumtungstate, lead cobalt niobate, or any combination of these.

Obviously, the emitter section may be composed of a material containing50 percent by weight or more of the above-described compound as the maincomponent. Of the ceramics described above, a ceramic containing leadzirconate is most frequently used as the constituent material for thepiezoelectric/electrostrictive layer that serves as the emitter section.

When the piezoelectric/electrostrictive layer is formed using a ceramic,the ceramic may further contain an oxide of lanthanum, calcium,strontium, molybdenum, tungsten, barium, niobium, zinc, nickel, ormanganese, or any combination of these oxides, or other compounds. Theceramic described above may further contain SiO₂, CeO₂, Pb₅Ge₃O₁₁, orany combination of these. In particular, a PT-PZ-PMN-based piezoelectricmaterial containing 0.2 percent by weight of SiO₂, 0.1 percent by weightof CeO₂, or 1 to 2 percent by weight of Pb₅Ge₃O₁₁ is preferable.

In detail, for example, a ceramic mainly composed of lead magnesiumniobate, lead zirconate, and lead titanate, and containing lanthanum orstrontium in addition to these Is particularly preferable.

The piezoelectric/electrostrictive layer may be dense or porous. Whenthe piezoelectric/electrostrictive layer is porous, the void ratio ispreferably 40% or less.

When an antiferroelectric layer is used as the emitter section 13, theantiferroelectric layer preferably contains lead zirconate as a maincomponent, lead zirconate and lead stannate as main components, leadzirconate containing lanthanum oxide as an additive, or a lead zirconateand lead stannate containing lead niobate as an additive.

The antiferroelectric layer may be porous. When the antiferroelectriclayer is porous, the void ratio thereof is preferably 30% or less.

In particular, strontium tantalate bismuthate (SrBi₂Ta₂O₉), whichundergoes low fatigue by repeated polarization reversal, is suitable forthe emitter section. The material exhibiting low fatigue is a laminarferroelectric compound represented by general formula(BiO₂)²⁺(Am_(m−1)B_(m)O_(3m+1))²⁻. In the formula, the ions of the metalA are Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Bi³⁺, La³⁺, or the like, and the ions ofthe metal B are Ti⁴⁺, Ta⁵⁺, Nb⁵⁺, or the like. Alternatively, apiezoelectric ceramic based on barium titanate, lead zirconate, or PZTmay be combined with an additive to impart semiconductive properties tothe ceramic. In such a case, since the emitter section 13 has an unevenelectric field distribution, it becomes possible to concentrate theelectric field near the interface with the upper electrode thatcontributes to electron emission.

The baking temperature of the emitter section 13 can be decreased byadding a glass component, such as lead borosilicate glass, or alow-melting-point compound (such as bismuth oxide) other than the glasscomponent to the piezoelectric/electrostrictive/antiferroelectricceramic.

In forming the emitter section with thepiezoelectric/electrostrictive/antiferroelectric ceramic, the emittersection may be formed from a molded sheet, a laminated sheet, or acomposite of the molded sheet or the laminated sheet stacked or bondedon a supporting substrate.

An emitter section that is hardly damaged by collision of electrons orions can be produced by using a material having a high melting point ora high evaporation temperature, e.g., a non-lead material, for theemitter section.

The emitter section may be formed by various thick-film formingprocesses, such as a screen printing process, a dipping process, anapplication process, an electrophoresis process, and an aerosoldeposition process; or by various thin-film forming processes, such asan ion-beam process, a sputtering process, a vacuum deposition process,an ion-plating process, a chemical vapor deposition (CVD) process, and aplating process. In particular, a powderedpiezoelectric/electrostrictive material may be molded to form theemitter section, and the molded emitter section may be impregnated witha low-melting-point glass or sol particles to form a film at atemperature as low as 700° C. or 600° C. or less.

Upper Electrode 14

An organometal paste that can produce a thin film by baking is used toform the upper electrode. An example of the organometal paste is aplatinum resinate paste. The upper electrode is preferably composed ofan oxide that can decrease the fatigue due to polarization reversal or aplatinum resinate paste containing an oxide for decreasing the fatigueby polarization reversal. Examples of the oxide that decreases thefatigue by polarization reversal include ruthenium oxide (RuO₂), iridiumoxide (IrO₂), strontium ruthenate (SrRuO₃), La_(1-x)Sr_(x)CoO₃ (e.g.,x=0.3 or 0.5), La_(1-x)Ca_(x)MnO₃ (e.g., x=0.2), andLa_(1-x)Ca_(x)Mn_(1-y)Co_(y)O₃ (e.g., x=0.2, y=0.05).

It is also preferable to use an aggregate of scale-like substances, suchas graphite, or an aggregate of conductive substances containingscale-like substances to form the upper electrode. Since such anaggregate has gaps between scales, the gaps can serve as the microthrough holes in the upper electrode, and thus no baking process isneeded to form the upper electrode. Alternatively, an organic resin anda metal thin film may be sequentially stacked on the emitter section andbaked to burn off the organic resin and to thereby form micro throughholes in the metal thin film, which serves as the upper electrode.

The upper electrode may be formed by various thick-film formingprocesses, such as a screen printing process, a spraying process, acoating process, a dipping process, an application process, and anelectrophoresis process; or by various-thin-film forming processes, suchas a sputtering process, an ion-beam process, a vacuum depositionprocess, an ion-plating process, a chemical vapor deposition (CVD)process, and a plating process.

As is described above, the electron-emitting apparatus of the presentinvention adequately controls the voltage (drive voltage) generated fromthe power supply and the constant of the circuit for applying the drivevoltage. Thus, unnecessary electron emission can be avoided.

By increasing the voltage (drive voltage Vin) generated either graduallyor stepwise-like as described above, the polarization reversal and theelectron emission are performed while the difference between the drivevoltage Vin and the element voltage Vka is small, Thus, powerconsumption (generation of joule heat) in and by the resistor componentsin the element and and the circuit resistors near the elements can bedecreased. As a result, the element is not heated, and the thus,properties of the emitter section can be prevented from being changed bythe heat. Since the element temperature does not increase, evaporationof the materials adhering onto the element can be avoided. This preventsgeneration of plasma, and thus, It is possible to avoid excessiveelectron emission (intense light emission) and damage on the element byion bombardment.

Each electron-emitting apparatus described above turns off the collectorelectrode when there is a possibility of occurrence of unnecessaryelectron emission and turns on the collector electrode when electronemission (proper electron emission) is necessary. Thus, theelectron-emitting apparatus can impart sufficient energy to electronsregularly and properly emitted while avoiding unnecessary electronemission, and provides a display that can present satisfactory images.Moreover, even when the space between the upper electrode 14 and thecollector electrode 18 enters a plasma state, the plasma can beeliminated since the collector electrode 18 is intermittently turnedoff. As a result, continuous generation of intense emission due to acontinuing plasma state can be avoided.

Since the focusing electrode is provided so that emitted electronssubstantially travel in the upward direction of the upper electrode, thedistance between the upper electrode and the collector electrode can beincreased. Thus, dielectric breakdown between the upper electrode andthe collector electrode can be reduced or prevented. Because thepossibility of dielectric breakdown between the upper electrode and thecollector electrode is low, the first collector voltage V1 (Vc) appliedto the collector electrode 18 during the period in which the collectorelectrode 18 is turned on can be increased. Thus, large energy can beimparted to the electrons reaching the phosphors, and the luminance ofthe display can be thereby increased.

Note that the present invention is not limited to the embodimentsdescribed above and various other modifications and alternations arepossible without departing from the scope of the invention. For example,as shown in FIG. 33, the focusing electrodes 16 may be formed not onlybetween the upper electrodes 14 adjacent to each other In the X-axisdirection but also between the upper electrodes 14 adjacent to eachother in the Y-axis direction in a plan view.

According to this arrangement, electrons emitted from the upperelectrode 14 of a particular element do not reach the phosphor disposedabove the upper electrode 14 of an adjacent element. Thus, color puritycan be satisfactorily maintained. In this example, the focusingelectrodes 16 are also disposed between the upper electrodes 14 of theelements adjacent to each other in the Y-axis direction. Thus, electronsemitted from the upper electrode 14 of a particular upper electrode 14do not reach the phosphor disposed above the adjacent upper electrode14. Thus, blurring of image patterns can be prevented.

Referring to FIG. 34, the electron-emitting apparatus may have one pixelPX including four elements (a first upper electrode 14-1, a second upperelectrode 14-2, a third upper electrode 14-3, and a fourth upperelectrode 14-4), and focusing electrodes 16. In such a case, forexample, a green phosphor (not shown) is disposed directly above thefirst upper electrode 14-1, a red phosphor (not shown) is disposeddirectly above each of the second upper electrode 14-2 and the fourthupper electrode 14-4, and a blue phosphor (not shown) is disposeddirectly above the third upper electrode 14-3. The focusing electrodes16 are formed to surround each of the upper electrodes 14. With thisarrangement, electrons emitted from the upper electrode 14 of aparticular element reach only the phosphor disposed directly above theupper electrode 14. Thus, satisfactory color purity can be maintained,and blurring of the image patterns can be prevented.

FIGS. 35 and 36 show another electron-emitting apparatus 60 according tothe present invention. The electron-emitting apparatus 60 may include aplurality of completely independent elements aligned on the substrate11, each element including a lower electrode 62, an emitter section 63,and an upper electrode 64. In this apparatus, the gaps between theelements may be filled with insulators 65, and focusing electrodes 66may be disposed on the upper surfaces of the insulators 65 between theupper electrodes 64 adjacent to each other in the X-axis direction.

In this electron-emitting apparatus 60, electrons can be emitted fromthe elements either simultaneously or at independent timings. Thus, anindependent collector electrode may be disposed above the upperelectrode 64 of the corresponding element, and the collector voltageapplying circuit may turn off or on the collector electrode based on thestatus of the element corresponding to the collector electrode.

Time-varying voltage Vs(t) may be applied to the focusing electrodes 16(66). In such a case, for example, a larger negative voltage may beapplied to the focusing electrode 16 during the charge accumulationperiod Td than in the emission period Th so that unnecessary electronemission can be more securely suppressed during the charge accumulationperiod Td.

Moreover, the focusing electrode 16 may be maintained in the floatingstate during the charge accumulation period Td, and a predeterminedpotential may be applied to the focusing electrode 16 during theemission period Th. In this way, generation of transient currentresulting from capacity coupling between the focusing electrode 16 andthe upper electrode 14 or between the focusing electrode 16 and thelower electrode 12 can be avoided, and thus, unnecessary powerconsumption can be avoided.

The substrate 11 may be composed of a material primarily composed ofaluminum oxide or a material primarily composed of a mixture of aluminumoxide and zirconium oxide.

Furthermore, various other experiments were conducted on theelectron-emitting apparatus. The experiments found that by reducing therising time T_(rise) (the time required for the drive voltage Vin at thefirst voltage Vm, which is the negative predetermined voltage forelectron accumulation, to reach the second voltage Vp, which is thepositive predetermined voltage for electron emission), the amount ofelectrons emitted properly from the electron-emitting element can beincreased. The meaning of “reducing the rising time T_(rise) of thedrive voltage Vin” is that the rate α of change in drive voltage Vin,i.e., dVin/dt or inclination, is increased.

FIG. 37 is a schematic diagram showing a measurement circuit used forstudying the relationship between the rising time T_(rise) of the drivevoltage Vin and the amount of electrons emitted. In this measurementcircuit, an electron-emitting apparatus 70 is used. As with theelectron-emitting apparatus 40 shown in FIG. 30, the electron-emittingapparatus 70 has an electron-emitting element including the lowerelectrode 12, the emitter section 13, and the upper electrode 14. Abovethe upper electrode-side of the element D, the collector electrode 18′,the phosphor 19′, and the transparent plate 17 of the electron-emittingapparatus 50 shown in FIG. 32 are disposed facing the upper electrode14.

The lower electrode 12 is connected to a terminal of a power supply(drive voltage applying circuit) 71 via a first resistor R1 and to thenegative electrode of a constant voltage source 72 for applying thecollector voltage Vc also via the first resistor R1. The positiveelectrode of the constant voltage source 72 is connected to thecollector electrode 18′ via a second resistor R2. The upper electrode 14is connected to another terminal of the power supply 71. An avalanchephoto diode (APD) is disposed above the transparent plate 17. The APDoutputs a voltage Vapd corresponding to the intensity of the lightoutput from the phosphor 19′.

As is described below, the power supply 71 generates a pulsed voltage.When electrons are emitted through the upper electrode 14 of the elementD, a collector current Ic flows in the direction indicated in FIG. 37.The collector current Ic is time-integrated over one pulse cycle, thepulse being generated by the power supply 71 to determine the totalamount SIc of electrons emitted in one light emission (electronemission). Similarly, the APD output voltage Vapd is time-integratedover one pulse cycle to determine the value SVapd corresponding to theintensity of light emitted in one light emission. The value SVapd issubstantially in proportion to the amount of electrons emitted. Thus, bycomparing the SVapd with the amount SIc of electrons emitted which isobtained by integration of the collector current Ic, one can confirmthat measurement of the amount SIc of electrons emitted can be conductedproperly and accurately.

FIG. 38 includes time charts showing the observed collector current Icand the APD output voltage Vapd while the drive voltage Vin is changedin various manners. In the measurement, the drive voltage Vin ismaintained at the first voltage Vm (−50 V, the negative predeterminedvoltage) for a predetermined period of time, i.e., about 4 ms. Duringthis period, electrons are accumulated in the upper portion of theemitter section 13. Subsequently, the drive voltage Vin is linearlyincreased toward the second voltage Vp (200 V, the positivepredetermined voltage) over the rising time T_(rise). The first resistorR1 has a resistance of 1 kΩ.

In FIG. 38, a line L10 shows the drive voltage Vin with zero (ms) risingtime T_(rise). A line M10 and a line N10 respectively show the collectorcurrent Ic and the APD output voltage Vapd when the drive voltage Vinindicated by the line L10 is applied to the element D. A line L11 showsthe drive voltage Vin with a rising time T_(rise) of 1 (ms). A line M11and a line N11 respectively show the collector current Ic and the APDoutput voltage Vapd when the drive voltage Vin indicated by the line L11is applied to the element D. Similarly, a line L12 shows the drivevoltage Vin with a rising time T_(rise) of 2 (ms). A line M12 and a lineN12 respectively show the collector current Ic and the APD outputvoltage Vapd when the drive voltage Vin indicated by the line L12 isapplied to the element D.

A line L13 shows the drive voltage Vin with a rising time T_(rise) of 4(ms). A line M13 and a line N13 respectively show the collector currentIc and the APD output voltage Vapd when the drive voltage Vin indicatedby the line L13 is applied to the element D. A line L14 shows the drivevoltage Vin with a rising time T_(rise) of 6 (ms). A line M14 and a lineN14 respectively show the collector current Ic and the APD outputvoltage Vapd when the drive voltage Vin indicated by the line L14 Isapplied to the element D.

FIG. 39 is a graph showing the relationship between the amount SIc ofelectrons emitted and the value SVapd plotted versus the rising timeT_(rise) of the drive voltage Vin observed in the same measurement.

FIGS. 38 and 39 show that the amount of electrons emitted increases asthe rising time T_(rise) of the drive voltage Vin is shorter (i.e., asthe rate α of change in drive voltage Vin is increased). The reason forthis is presumably as follows.

When the first voltage Vm, i.e., the negative predetermined voltage, Isapplied to the element D, electrons are accumulated in or on the surfaceof the emitter section 13 (electrification). When the second voltage Vp(light-ON voltage or electron emission voltage), which is the positivepredetermined voltage, is subsequently applied to the element D, thedipole in the emitter section 13 becomes reversed (polarizationreversal). This causes part of the electrons accumulated in or on thesurface of the emitter section 13 to travel along the upper portion ofthe emitter section 13 (the portion in which surface resistance isgenerated) and to eventually be captured (collected) by the portion ofthe upper electrode 14 in contact with the emitter section 13. The restof the electrons are emitted in the upward direction of the emittersection 13. In addition, some electrons emitted upward are captured(collected) by the upper electrode 14, and only the remaining electronsreach the collector electrode 18′.

On the other hand, as the rising time T_(rise) of the drive voltage Vinbecomes shorter, the speed of the polarization reversal becomes higher.Thus, before the accumulated electrons travel in or on the upper portionof the emitter section 13 and captured (collected) by the upperelectrode 14, the electrons accumulated in the upper portion of theemitter section 13 receive rapidly increasing repulsive force from alarge number of dipoles (negative poles of dipoles) that underwent rapidpolarization reversal in the upper portion of the emitter section 13 andare thus emitted in the upward direction from the emitter section 13. Asa result, the amount of the electrons emitted in the upward directionfrom the emitter section 13 increases.

Furthermore, the electrons emitted in the upward direction from theemitter section 13 are significantly accelerated due to high-speedpolarization reversal. Thus, the initial speed of the electrons emittedis high. Consequently, the ratio of the electrons captured (collected)by the upper electrode 14 to the electrons emitted in the upwarddirection from the emitter section 13 decreases, and the ratio of theelectrons emitted upward through the micro through holes in the upperelectrode 14 increases.

As Is described above, as the rising time T_(rise) of the drive voltageVin is shortened, the ratio of the electrons traveling in the upperportion of the emitter section 13 and being captured (collected) by theupper electrode 14 decreases, and thus, the ratio of the electronsemitted in the upward direction from the emitter section 13 increases.Moreover, the ratio of the electrons captured (collected) by the upperelectrode 14 among the electrons emitted in the upward direction fromthe emitter section 13 decreases. These phenomena are presumably thereasons (causes) why the amount of electrons emitted are increased. Notethat when the first resistor R1 is set to 1 kΩ as above and the risingtime T_(rise) of the drive voltage Vin is set to 0 (ms), the actualrising time is 0.15 (ms) due to the first resistor R1. When the firstresistor R1 is set to 500 Ω and the rising time T_(rise) of the drivevoltage Vin is set to 0 (ms), the actual rising time is 0.1 (ms). Thisis shorter than when the resistance of the first resistor R1 is set to 1kΩ. As shown in FIG. 39, when the rising time T_(rise) of the drivevoltage Vin is set to 0 (ms), the actual rising time is shorter with thea 500 Ω first resistor R1 than with a 1 kΩ first resistor R1. Thus, theamount SIc of the electrons emitted is increased. This result isconsistent with the conclusion discussed above.

1. An electron-emitting apparatus comprising: an element including: an emitter section composed of a dielectric material, a lower electrode disposed below the emitter portion, and an upper electrode that is disposed above the emitter section to oppose the lower electrode with the emitter section therebetween, the upper electrode having a plurality of micro through holes; and drive voltage applying means including: a power supply, and a circuit for applying a voltage, which is generated by the power supply, between the lower electrode and the upper electrode, wherein the power supply is configured to generate a first voltage to cause an element voltage to converge on a negative predetermined voltage so that electrons are supplied from the upper electrode to the emitter section and accumulated in the emitter section, and to subsequently generate a voltage which gradually increase toward a second voltage to cause the element voltage to converge on a positive predetermined voltage so that the electrons accumulated in the emitter section are emitted from the emitter section, the element voltage being a potential difference between the lower electrode and the upper electrode with respect to a potential of the lower electrode.
 2. The electron-emitting apparatus according to claim 1, wherein the power supply is configured such that, after generation of the first voltage, the power supply generates a voltage increasing from the first voltage to a third voltage so that the element voltage is caused to be an intermediate voltage between the negative predetermined voltage and the positive predetermined voltage, the intermediate voltage causing neither further electron accumulation in nor electron emission from the emitter section; and subsequently, the power supply generates a voltage increasing from the third voltage to the second voltage at a rate lower than a rate at which the voltage is increased from the first voltage to the third voltage.
 3. The electron-emitting apparatus according to claim 1, wherein the power supply is configured such that, within a period from a time point at which generation of the voltage gradually increasing toward the second voltage is started to a time point at which the voltage reaches the second voltage, the power supply generates a voltage that increases at a lowest rate during a period from the time point at which the generation of the voltage gradually increasing toward the second voltage is started to a time point at which positive-side polarization reversal in the emitter section is substantially completed.
 4. The electron-emitting apparatus according to claim 1, wherein the power supply is configured such that, within a period from a time point at which generation of the voltage gradually increasing toward the second voltage is started to a time point at which the voltage reaches the second voltage, the power supply generates a voltage that increases at a lowest rate during a period from a time point at which positive-side polarization reversal in the emitter section is substantially completed to the time point at which the voltage reaches the second voltage.
 5. An electron-emitting apparatus comprising: an element including: an emitter section composed of a dielectric material, a lower electrode disposed below the emitter portion, and an upper electrode that is disposed above the emitter section to oppose the lower electrode with the emitter section therebetween, the upper electrode having a plurality of micro through holes; and drive voltage applying means including: a power supply, and a circuit for applying a voltage, which is generated by the power supply, between the lower electrode and the upper electrode, wherein the power supply is configured to generate a second voltage to cause an element voltage to converge on a positive predetermined voltage so that electrons accumulated in the emitter section is emitted from the emitter section, and to generate subsequently a voltage which gradually decrease toward a first voltage to cause the element voltage to converge on a negative predetermined voltage so that the electrons are supplied from the upper electrode to the emitter section and accumulated in the emitter section, the element voltage being a potential difference between the lower electrode and the upper electrode with respect to a potential of the lower electrode.
 6. The electron-emitting apparatus according to claim 5, wherein the power supply is configured such that, after generation of the second voltage, the power supply generates a voltage decreasing from the second voltage to a third voltage so that the element voltage is caused to be an intermediate voltage between the negative predetermined voltage and the positive predetermined voltage, the intermediate voltage causing neither electron accumulation in nor electron emission from the emitter section; and subsequently the power supply generates a voltage decreasing from the third voltage to the first voltage at a rate lower than a rate at which the voltage is decreased from the second voltage to the third voltage.
 7. The electron-emitting apparatus according to claim 5, wherein the power supply is configured such that, within a period from a time point at which generation of voltage gradually decreasing toward the first voltage is started to a time point at which the voltage reaches the first voltage, the power supply generates a voltage that decreases at a lowest rate during a period from the time point at which the generation of the voltage gradually decreasing toward the first voltage is started to a time point at which negative-side polarization reversal in the emitter section is substantially completed.
 8. The electron-emitting apparatus according to claim 4, wherein the power supply is configured such that, within a period from a time point at which generation of voltage gradually decreasing toward the first voltage is started to a time point at which the voltage reaches the first voltage, the power supply generates a voltage that decreases at a lowest rate during a period from a time point at which negative-side polarization reversal in the emitter section is substantially completed to the time point at which the voltage reaches the first voltage.
 9. The electron-emitting apparatus according to claim 1, wherein: the power supply is configured to repeat generation of the first voltage and the second voltage in an alternating manner, and the drive voltage applying means includes circuit parameter setting means for setting a circuit parameter of the circuit by connecting a circuit element to the circuit, the circuit element selected from: a first circuit element that is inserted into the circuit during a first period from a time point at which the generation of the voltage decreasing toward the first voltage is started to a time point at which the negative-side polarization reversal in the emitter section is substantially completed while the voltage is decreased, a second circuit element that is inserted into the circuit during a second period from the time point at which the negative-side polarization reversal in the emitter section is substantially completed to a time point at which electron emission in the emitter section is completed, a third circuit element that is inserted into the circuit during a third period from a time point at which generation of the voltage increasing toward the second voltage is started to a time point at which the positive-side polarization reversal in the emitter section is substantially completed while the voltage is increased, and a fourth circuit element that is inserted into the circuit during a fourth period from a time point at which the positive-side polarization reversal is substantially completed to a time point at which electron emission from the emitter section is substantially completed, wherein at least two of these circuit elements are different from each other.
 10. An electron-emitting apparatus comprising: an element including: an emitter section composed of a dielectric material, a lower electrode disposed below the emitter portion, and an upper electrode that is disposed above the emitter section to oppose the lower electrode with the emitter section therebetween, the upper electrode having a plurality of micro through holes; and drive voltage applying means including: a power supply which is configured to generate a first voltage to cause an element voltage to converge on a negative predetermined voltage so that electrons are supplied from the upper electrode to the emitter section and accumulated in the emitter section, and to subsequently generate a voltage which gradually increase toward a second voltage to cause the element voltage to converge on a positive predetermined voltage so that the electrons accumulated in the emitter section are emitted from the emitter section, the element voltage being a potential difference between the lower electrode and the upper electrode with respect to a potential of the lower electrode, and a circuit for applying the voltage generated by the power supply between the lower electrode and the upper electrode, wherein: the power supply is configured to repeat generation of the first voltage and the second voltage in an alternating manner, and the drive voltage applying means includes circuit parameter setting means for setting a circuit parameter of the circuit by connecting a circuit element to the circuit, the circuit element selected from: a first circuit element that is inserted into the circuit during a first period from a time point at which the generation of the voltage decreasing toward the first voltage is started to a time point at which the negative-side polarization reversal in the emitter section is substantially completed while the voltage is decreased, a second circuit element that is inserted into the circuit during a second period from the time point at which the negative-side polarization reversal in the emitter section is substantially completed to a time point at which electron emission in the emitter section is completed, a third circuit element that is inserted into the circuit during a third period from a time point at which generation of the voltage increasing toward the second voltage is started to a time point at which the positive-side polarization reversal in the emitter section is substantially completed while the voltage is increased, and a fourth circuit element that is inserted into the circuit during a fourth period from a time point at which the positive-side polarization reversal is substantially completed to a time point at which electron emission from the emitter section is substantially completed, wherein at least two of these circuit elements are different from each other.
 11. An electron-emitting apparatus comprising: an element including: an emitter section composed of a dielectric material, a lower electrode disposed below the emitter portion, and an upper electrode that is disposed above the emitter section to oppose the lower electrode with the emitter section therebetween, the upper electrode having a plurality of micro through holes; and drive voltage applying means including: a power supply, and a circuit for applying a voltage, which is generated by the power supply, between the lower electrode and the upper electrode, wherein the power supply, in order to supply electrons from the upper electrode to the emitter section and to accumulate the electrons in the emitter section, is configured to generate a fourth voltage which is a negative voltage to cause polarization reversal in the emitter section, then to generate a fifth voltage, which is a negative voltage whose absolute value is smaller than the absolute value of the fourth voltage, at a time point at which the polarization reversal is substantially completed or before the completion of the polarization reversal, and then to generate a voltage which gradually decreases toward a first voltage and which is a negative voltage whose absolute value is larger than the absolute value of the fifth voltage. 